Full text of "Carburation in theory and practice, including a criticism of carburettor development; a manual of reference for automobile engineers and owners"

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CARBURATION IN THEORY AND
PRACTICE

BY THE SAME AUTHOR

250 pages, with numerous Ilhistratlons, detny Bvo, cloth
Price 5s. net

MOTOR CAR CONSTRUCTION

A Practical Manual for Engineers, Students,

and Motor Car Owners, with Notes on Wind

Resistance and Body Design

" Tlie book should find a place on the shelves of every student
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" Any book on a subject connected with automobilism from the
pen of ^Ir Robert W. A. Brewer is worthy of the closest study, for
the author is a well-known authority on all matters relating to
motor cars, their construction and management." — Royal Auto-
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THE ART OF AVIATION

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With numerous Illustrations and dimensioned Draiuings

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LONDON: CROSBY LOCKWOOD AND SON

■^ y^ ■ — » ->t X ..^ID .yz >/' j^/v ^N

CARBURATION

THEORY AND PRACTICE

3nclu&ing a Criticiem of Carburettor Development

A MANUAL OF REFERENCE FOR AUTOMOBILE
ENGINEERS AND OWNERS

ROBERT W? aK BREWER

FELLOW OF THE SOCIETY OF ENGINEERS (gOLo'iIIEDALLIST AND BESSEMER

1'Rizeman); assoc.m.inst.c.e. ; m.i.mech.e. ; m.i. automohile e. ; .member

OF the society of automobile engineers; author OF ".MOTOR CAR

construction"; "the art of aviation"

TKttitb numerous 5llU6tration6, {Tables, aiiD ©tasrams

(2piom]ai

LONDON

CROSBY LOCKVVOOD AND SOX

7 STATIONERS' HALL COURT, E.G.
AND 5 BROADWAY. WESTMINSTER, S.W.

1913

~EIA

635097

PREFACE

The subject of carburation is one which is vital
to the automobile movement and has, therefore,
received more scientific attention during the past
few years. This has been necessary on account of
the demands of the public for wide ranges of engine
speed, controllability, and quietness.

The author has been unable to discover much
scientific book work dealing with this subject, with
the exception of that very useful book of Sorel's
upon the subject of alcohol motors. There is, un-
doubtedly, a considerable interest taken, both by
automobile engineers and owners, in the carburettor
question, and this has been much greater recently
on account of the increased price of fuel.

It is the intention of the author that this book
should provide in convenient form information upon
the properties of various fuels, how the said fuels
require treatment for use in a motor car engine, and

PREFACE

what has been done in the past in order to obtain
the necessary data upon which to base the theory.

The user will find much information which will
give him a clearer understanding of the principles of
carburation and enable him to effect economies in
working, and the designer should be saved many
hours of labour by the use of the data contained
herein.

The closing chapters consist of descriptions of
some of the best known carburettors, with criticisms
thereon, but the number of carburettors which has
been produced is so large that it is impossible to
include all.

A certain amount of the information contained
herein has been embodied in lectures and papers and
press contributions, and is reproduced in a slightly
different form by kind permission of the editor of
the Automobile Enginee7% now Internal Co7nbustion
Engineering, and the editor of the Automobile of
America.

TABLE OF CONTENTS

PART I

CHAPTER I

PAGES

General Outline ------ 1-9

r CHAPTER II

Vaporisation and P2vaporation - - - 10-19

CHAPTER III
Limits of Combustion— Air and Heat Required - 20-35

CHAPTER IV

Inlet Pipes and Inertia . - - . 36-47

CHAPTER V

The Flow of Fuel through Small Orifices - 48-72

CHAPTER VI
The Annui.us ...--. 73-82

CHAPTER VII
Brewer's Fuel Orifice ----- 83-99

CHAPTER VIII
Special Jets ------ 100-105

VIU

TABLE OF CONTENTS

Moving Parts

Float Chambers

Petrol Substitutes

CHAPTER IX

CHAPTER X

CHAPTER XI

CHAPTER Xn

Exhaust Gas Analyses

}'AGES
IO6-II5

II 6- I 22

123-140

I4I-I49

PART II
CHAPTER XHI

Carburettors

151-240

APPENDIX I

TABLE LVI

Equivalents

241

TABLE LVU

Conversion from Degrees Baume to Specific Gravity 242

TABLE LVni

Properties of Gases .... Facing page 242

APPENDIX II

Notes from a Paper^by Mr G. H. Baillie -
INDEX

242-246
247-253

CARBURATION

■^>K-

PART I

CHAPTER I

GENERAL OUTLINE

By the use of the word " carburation," it must be under-
stood that this word will designate the art of mechanically
mixing or blending a liquid fuel with a certain amount of
air, aitd that whether this art is carried out to the limits of
perfection or not, is an indication of whether the carbura-
tion is good or bad. Carburation will be considered to be
more or less complete by reason of the manner in which
the air is mixed with the molecules of the liquid fuel, or
whether the fuel is divided into its finest possible particles
in such a way that every particle of fuel is surrounded by
a certain quantity of air to the limit of homogeneity of the
mixture.

Homogeneity signifies " having the same properties or
character in every direction." A homogeneous fuel is one
of uniform composition throughout, so that samples taken,
however large or small, from any part of the bulk of the
fuel are exactly alike in composition. As far as the
explosive mixture supplied to an engine is concerned, if
two gases are the active agents, such as coal gas and air
or oxygen, the intimate mixing of these in the inlet

CARBURATION

■

arrangements, combined with the turbulence in the cylinder
during the compression stroke, result in a fairly homo-
geneous mixture at the moment of ignition. There are
special cases, however, in which such is not the case, and
where stratification is aimed at. This result can be
obtained to some extent when special provision is made.

The motor car engine using liquid fuel does not,
however, require a stratified mixture, but a homogeneous
one, as will be seen later on, and in order to obtain this
the carburettor should be designed for that end, 4^1

Another term which will frequently be used is that of
" depression at the orifice," or " head over the orifice,"
expressed in inches of water. This means that the differ-
ence of pressure between that of the atmosphere and that
adjacent to the fuel orifice is sufficient to support a column
of water the number of inches in height which is expressed.
Saturation of air by a vapour occurs when the air is unable
to support any more vapour in that form, so that the addition
of vapour causes precipitation of the liquid from which the
vapour has arisen.

Raising the temperature of the mixture will, however,
allow the air to retain a greater percentage of vapour, as
will also a reduction of pressure.

Fuel is discussed as containing a certain number of
" fractions " or constituents which distil off as the tempera-
ture of the fuel is raised. Petroleum spirit consists of many
different hydrocarbons, and in specifying any spirit, its final
boiling or distillation point is one of the most important
factors, together with the percentage of the total quantity
of the fuel distilling off at different temperatures.

The " lighter fractions " designate the more volatile
benzines of the hexane series when referred to motor spirit,
but with reference to crude oil may imply all those con-
stituents distilling below 150° C, which usually comprise
commercial motor spirit.

Fuel may be mixed with air in several ways. The first
and the oldest form of carbu ration is by passing the air

EXPLANATION OF TERMS 3

through a volume of liquid fuel. On the other hand, the
volume of air can be treated by spraying into it a certain
quantity of fuel in a more or less finely divided state.
There is another form of carburation, which is virtually
distillation or evaporation by means of applied heat, and
it is quite conceivable that if a volume of air is passed
over a liquid, and a higher temperature than the normal
is applied to this liquid, the evaporation of the liquid will
be accelerated above what it is under ordinary atmospheric
conditions. Assuming that the rate of evaporation of the
fuel is in proportion to the amount of air passing, and that
the air is brought sufficiently near to the surface of the
fuel, a satisfactory form of carburation will follow.

It is naturally somewhat difficult, when dealing either
with air or with fuel in quantities, to obtain a homogeneous
result in the mixture. For this reason it is preferable to
treat small quantities as desired ; furthermore, when small
quantities of air and fuel are dealt with, there is not so
much risk of accident from any involuntary ignition of
the explosive mixture in the generating chamber, as is the
case where a larger volume is dealt with in a chamber of
considerable capacity.

An engine such as is used in the modern motor vehicle
is not running under constant demand, and it is therefore
preferable to create an explosive mixture in accordance
with the demands of the engine, rather than to store up
any quantity of explosive mixture to meet any sudden
demand which may come upon the engine. In this
practice we are more nearly approaching the modern trend
in stationary gas engine practice, where a suction producer
is fitted, and the suction producer in that case corresponds
to the carburettor of an engine, rather than to the gas
holder which was previously used when coal gas was
employed. We find in a gas set, where the engine sucks
directly upon the carburettor, the amount of carburetted
air which is drawn in is in direct response to the demands
of the engine.

CARBURATION

There is probably no part of a modern motor car which
has undergone more useful development in recent years
than the carburettor. The improvements which have taken
place' have made it possible to obtain that great range of
speeds of engine rotation with which we are all now
familiar. Furthermore, these results have been accom-
panied by other advantages, such as the reduction of
petrol consumption, more perfect combustion, the preven-
tion of overheating, and ease of starting.

When we come to investigate how these ends have
been obtained, we find that there is no one method or
principle which stands out with prominence beyond several
others. This fact cannot be disputed, as the result of
numerous severe competitive tests show. It may be that,
as a result of a series of trials undertaken by one firm of
motor car manufacturers, a particular carburettor suits a
particular engine somewhat better than other competing
carburettors, on all-round results. In another instance we
may find again that a different carburettor, working upon
an entirely different principle, is more suitable to another
class of engine of approximately the same size. It is a
particularly interesting fact that such good results as have
been obtained recently should have been possible with
different instruments.

Let us revert for a moment to the early types of jet
carburettors in which the fuel supply to the engine was
more or less controlled by the size or number of the jet
orifices. This type of instrument, it will be remembered,
was fitted with a choke tube, either of one constant
diameter located round the jet orifice, or with a conoidal
tube, the position of which could be varied with regard to
the jet. Taking the first one as exemplified by the old
Longuemare, this tube was surrounded by an annulus
through which supplementary air was admitted by a hand-
controlled device. The arrangement was crude, as it was
only capable of giving a correct mixture automatically for
the one speed for which the choke tube was suited. As the

EARLY DEVICES 5

Speed increased so did the suction, and this latter had to
be counteracted by the admission of air from an external
source. It will be remembered that in these early devices
extra air valves working against springs were often pro-
vided to reduce the amount of hand manipulation necessary
with such an instrument

The early Krebs sought to combine the extra air valve
with the carburettor by means of air pressure actuating a
diaphragm against the resistance of a spring, and in such
an arrangement it is possible to design the air ports so that
the jet is surrounded by a constant pressure difference with
regard to the external atmosphere. A further development
of this principle was claimed in the Gillet-Lehmann device,
in which a direct connection was made by means of a small
pipe between the float chamber and the induction pipe at
one or more points. Assuming that the restricting screw
or screws were set properly, with a device of this nature
it was possible to regulate the pressure difference under
which the instrument worked with some degree of nicety.
Looking at the matter from the point of view not usually
apparent, we may consider that all devices of this nature
were forerunners of what are now known as constant
vacuum carburettors, and these in detail will be dealt with
later.

Again going back to the early days, we can call to mind
another line of development, which aimed at restricting the
efflux of the liquid fuel as the engine suction increased.
Such devices took the form of spirals or bears' poles of
metal in the jet orifice. Obviously arrangements of this
sort could scarcely be predetermined with regard to their
detail so as to give any great accuracy in working, and
their effect as regards uniform carburation at all speeds
could only be arrived at by means of trial and error.
These devices were undoubtedly the forerunners of some
of the instruments of to-day, in which the main feature is
the variation of jet orifice in accordance with the demands
of the engine^ The modern form of such an instrument is

6 CARBURATION

designed so that the orifice consists of at least two parts,
which rotate relatively to each other, and in which the
holes or orifices are circular, segmental, triangular, or any-
suitable shape, and which give an orifice opening in pro-
portion to the air and throttle opening.

Instruments of this type can be designed previously
with a great degree of accuracy, and require very little
final adjustment. There are, however, further develop- flj
ments of these instruments working in conjunction with
additional air devices, the latter controlled either pneu-
matically or hydraulically, which in modern designs can be
arranged to give excellent results. In such a combination,
however, more than one type of adjustment is required, and
the instrument immediately becomes liable to derangement
and erratic working in the hands of the inexperienced user.
Furthermore, the air-controlling arrangement is liable to
suffer as the operating mechanism wears, the spring control ,
loses its original liveliness, or the moving parts stick or
become loosened.

Now it is very obvious from general principles obtaining
in nature, where a body is turned from one state into
another, />., either from a solid to a liquid state or from a
liquid to a gaseous state, a certain amount of interchange
of heat must take place in order to effect this change
of state, and the amount of heat absorbed is, of' course, fl
in proportion to the latent heat of the body. In the
case of a liquid such as petroleum spirit, which is of a
complex nature, one cannot exactly state what its latent
heat of evaporation is, but it is of the order of i6o calories
per kilogram, equal to 288 B.Th.U. per pound of fuel
evaporated ; that means to say, that every pound of
petroleum spirit which is passed through the carburettor
requires an addition of heat equal to 288 British thermal
units in order to evaporate it so that the resulting
mixture shall remain at the same temperature as the
incoming air. This heat can be applied in several ways,
either by raising the temperature of the incoming air by

GENERAL PRINCIPLES 7

drawing that air over, say, the exhaust pipe, or by heating
the induction pipe between the mixing chamber of the
carburettor and the engine valves. Heat can also be
added to the liquid fuel itself before mixing with the air,
but such heating has its limitations by reason of the vola-
tility of the fuel and the low boiling point of some of its
fractions. It does not really signify how the heat is added
as long as the temperature of the resulting mixture remains
what is desired. By this latter expression, of course, a
great deal depends upon the locality, and the duty which
the car has to perform, and theoretically it is more suitable
for the temperature of the incoming mixture to be as low
as possible consistent with the liquid remaining in the
evaporated or suspended state without precipitation.

There is one point in connection with carburation which
is very frequently referred to, but about which very little
useful data is obtainable. This point is the effect of the
inertia of the liquid in the jet and passage leading thereto.
In those types of carburettors fitted with a modulating pin,
the inertia of the liquid is negligible, as there are more
important details than the flow of the fuel which are
affected by inertia. Take, for instance, the Stewart instru-
ment : there is bound to be a certain amount of lag in its
action as the moving part has considerable mass, and,
when the throttle is opened, this mass must respond both
against the action of gravity and its own dashpot. When
the throttle is closed there is again a certain lag, but owing
to the fact that the valve is off its seat there is an area
for air-flow considerably greater than the normal. The
result is, that owing to the decreased suction very little
petrol will be drawn up the centre tube, and the presence
of the pin will further baffle the flow of liquid to the centre
tube. Conversely, when the throttle is opened rapidly a
desirable state of affairs is reached, namely, a large suction
is produced at the jet during the time the valve is rising
to its normal position, and a correspondingly increased
richness of mixture follows. This richness enables the

CARBURATION

engine to pick up quickly, owing to the known fact that a
rich mixture, within certain Hmits, produces a more power-
ful explosion.

So-called constant suction carburettors are not really
by any means operating under the conditions indicated by
their title, as the suction is continually varying, but not in
the manner that it does in the ordinary jet and choke tube
instruments. For instance, one may calculate out and find
in practice that a certain carburettor will operate normally
under a certain depression, and this depression will usually
occur when the throttle is almost closed and the engine
running slowly. However, if the throttle be open the
value of the depression immediately decreases until a con-
dition of stability is reached when the engine is running at
a speed corresponding with its throttle opening. It will be
found that in practice the depression is not the same as
before, and, as the engine speed increases, the difference in
pressure inside and outside the carburettor has undergone
further slight but perceptible changes, which vary in accord-
ance with the design of the particular carburettor. The
changes of depression are most important, as, if the value
reaches too low a point, it is practically impossible for the
carburettor to pass sufficient petrol through its jet properly
to carburate the amount of air passing.

One must bear in mind that although high efficiency is
aimed at in the design of a carburettor working under a
small depression, there is a certain limiting size of orifice
beyond which it is inexpedient to go, on account of the
difficulty of getting sufficient petrol through it when the
engine demand is high. The author has had several diffi-
culties of this nature quite recently, and it would appear
that in practice the experimental feature is borne out with
regard to the falling off in the ratio of petrol flow to area
of orifice as the area of the orifice increases above the
maximum desirable size before referred to.

In the types of carburettors using a modulating pin, one
is able to take advantage of two fairly easily controllable

MODERN REQUIREMENTS 9

factors, namely, the positively varying jet orifice and the
possibility of suiting the air opening to any particular type
or size of engine. This latter feature is a most important
one when what is known as " high efficiency " work is
concerned. The details necessary for the fundamental
principles of design of the air aperture will vary with each
particular job, and depend, of course, upon valve areas,
compression spaces, and so forth, which have a bearing
upon the particular results aimed at.

A desirable feature in modern carburettors is that of
easy starting, and this is frequently attained by the use of
a starting well. This well may consist of a certain volume
of liquid, which at other times may be used as a dashpot
for the moving element of the carburettor, or, on the other
hand, may be a volume of petrol standing in a tube above,
or adjacent to, the actual jet orifice.

A good deal is often made of the necessity for the
ability to vary a carburettor to suit climatic conditions or
those of temperature, and details as to why this becomes
necessary are given in a later chapter. The automatic car-
burettor of the varying jet type is the easiest to alter to suit
special conditions, and, in addition to the modulating pin
scheme, there is that in which a number of similar jets are
uncovered by a predetermined plunger method. Such an
instrument is at once one that adapts itself automatically
to a wide range of demand, and embodies the necessity for
a large area for high speed work, with the concentration of
air-flow necessary for starting and slow running. Further-
more, this instrument embodies a combination adjustment
which acts throughout its entire range of working in the
same proportion, and when the flow of fuel is set for one
speed or working position, it remains correct for all other
positions.

CHAPTER II
VAPORISATION AND EVAPORATION

It has been pointed out that in changing a body from one
state to another, such as from a liquid to a gas, heat is
required to be applied, and the amount of such heat in any
particular case is the latent heat of evaporation of the
liquid.

In the case of water, if we have i lb. of this liquid at a
temperature of 212° F., and convert the whole of it into
steam at the same temperature and without loss of heat, an
addition of 966 B.Th.U. will be required. This heat, it will
be seen, is 6.35 times the heat required to raise the tempera-
ture of the same body of water from 60° F. to boiling point.

Liquid fuels, however, have a lower latent heat of
evaporation than water, as will be seen from the following
table : —

Table I. — Latent Heat of Evaporation of Liquids.

B.Th.U. per lb.

Calories per Kilogr.

Water - - - -

Hexane

0.700 sp. gr. petrol

Benzol

Commercial alcohol

966
210

250-288
232
520

244

53
63-72

58
130

We will now proceed to consider the characteristic
properties of fuels to be dealt with, and this can be done in
a more concise manner by means of a few tables. First,
taking the petroleum series of hydrocarbons represented by
C.H,

^2n-f2

SOME PROPERTIES OF FUELS

Table II.-

-(Sorel).

Name.

Formula.

Boiling Point.

Specific Gravity at
Temperature Indicated.

Degrees C.

Hexane*

^6^U

69-71

0.663 at 17

Heptane^

C7H16

0.668 „ 15

^ ^ ( normal* -

Octane < . ^^

( isomere*

^8"l8

124

0.719 „ 0

...

II9-I2O

0.719 „ 17

Nonane*

1 C()Hoo 1

149.5

0-723 » 13-5

» t - -

135-137

0.742 „ 12

Decane

^10"22

158-159

0.736 „ 18

Undecane -

C11H04

180-182

0.756 „ 16

Dodecane -

^'12 "26

214.5

0-755 V 15

Tredecane -

^13^28

218-220

0.778 „ 15

Tetradecane -

^14"30

236-240

0.796

Pentadecane-

' ^15 "32

258-262

0.809

* Chief constituents of motor spirit.

t And onwards, chief constituents of kerosene.

Next we will consider the distillation of a typical

motor spirit : —

'I'able III. — (Sorel).

Tenths.

Temperature.

Specific Gravity

Substance Collected.

Deg. Cent.

53
58

0.649
0.647

0.653 '

0.678

0.666

Pentane and hexane.

4
5

63
67

7
8

89
120

0.673 1
0.686 1
0.698

0.715

Hexane and heptane.

Heptane and octane.
Octane.

0.655

Pentane.

0.664

Hexane.

4
5

77
84

0.676
0.688
0.701

Hexane and heptane.

lOI

0.713

7
8

112
123

0.726 ^
0.814 >

Nonane and decane.

160

0.749 J

CARBURATION

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VALUES OF VAPOUR PRESSURES
Table V. — Kerosene (Sorel).

Tenths.

Temperature.

Specific
Gravity.

Substances Collected.

I
2

3
4

Deg, Cent.

138 to 177

177 „ 197

197 „ 212
212 „ 236
236 „ 253
253 » 274

0-755
0.765

0.776

0.783
0.796

0-795

Nonane to undecane

Undecane to dodecane

Dodecane to tredecane

Tredecane to tetradecane

Tetradecane

Pentadecane and hexadecane

It will thus be seen that the composition of motor
fuels of the petroleum series is somewhat complex and
does not bear out any definite rule, but that the proportion
of the lightest constituents is such that they are sufficient,
under ordinary circumstances, to effect a fair proportion
of the necessary carburation when the air is cold. As it is
better in a good system of carburation to vaporise the liquid
completely before introducing it into the engine, the quan-
tity of the air supplied depends both on the composition
of the fuel and on its vapour pressure and temperature.

■'''Table VI. — (Sorel). — Vapour Pressures of Different
Fuels in mm. of Mercury (Experimental).

Tempera-
ture.

Ilexane.

1
Automobiline.

Motonaphtha.

Benzol.

Kerosene.

Deg. Cent.

152

115

170

133

191

154

214

119

179

240

154

210

260

184

251

292

120

228

301

345

156

276

360

413

188

335

422

496

224

401

493

575

271

482

561

660

326

567

648

768

390

See also Appendix

CHAPTER III

LIMITS OF COMBUSTION— AIR AND

REQUIRED

In the case of an ordinary mixture of hydrocarbon vapour
and air there are two limits, an upper and a lower, between
which such a mixture will be combustible under normal
conditions. The completeness of combustion depends
upon the correct proportioning of air to fuel and whereas
the fuel may be in excess and CO be formed as a pro-
duct of combustion, if air be in excess the exhaust gases
will show O2 to be present. Under the same conditions of
temperature and pressure the mixture is non-flammable
outside certain limits, but it depends upon the temperature
and pressure and their variations, to which the explosive
mixture is submitted, as well as upon its initial composition,
as to where these limits will be found. If the mixture is
homogeneous, combustion will be complete within definite
limits, whilst outside them either the mixture will be
non-flammable or the combustion will be incomplete.

If combustion takes place in a long tube, and the
combining gases are slow-burning, such as CO and O,
and the ignition takes place at one end of the tube, the
propagation of the flame is slow and easily followed by
the eye.

If, however, a jet of flame from the same mixture be
projected through the entire mass of the mixture, com-
bustion is complete and rapid. This experiment shows
that rapiditj?^ of the propagation of the flame can be pro-
duced by arranging the ignition in a pocket in such a
manner that the richer gas, say over the inlet valve upon

LIMITS OF COMBUSTION 21

ignition, strikes a flame across the combustion chamber,
thus causing turbulence and accelerating combustion.

Now we will consider an example of the combustion
of methane, or natural gas and air, and Coquillion found
that I vol. of CH^ and 5 of air were non-explosive when
subjected to an electric spark, a i to 6 mixture gave the
inferior explosive limit due to insufficient air. When
the proportion of air was increased by 7 to 10 to i vol. of
methane the maximum pressures were reached. As the
air was increased so as to be 15 vols, to i of methane
the explosion weakened off, till at a 16 to i mixture the
upper limit was reached when no ignition occurred. These
mixtures were only at atmospheric pressure, and the upper
limit can be further extended as the initial pressure is
increased. One of the principal objects of compression is
to enable a weak mixture to be fired, which under atmos-
pheric pressure is non-explosive. Dilution of a mixture
either by air or inert gas results in the excess of such gas
absorbing part of the liberated heat of combustion, and so
fixes the limit between explosion and non-explosion, and
also the line between the zone of non-explosion and
apparent equilibrium.

Sorel's experiments with pure benzene, the coal-tar
product, were made at atmospheric pressure and at a
temperature of 100° C. Theoretically requiring 10.71
litres of dry air at 10" C. per grm. of benzene for complete
combustion, the upper limit through excess of air was
reached when the air introduced was 2.2 times the
theoretical quantity. The inferior limit through excess
of fuel was very low, as combustion continued when the
air was cut down to 0.27 times the theoretical amount.

Experiments with light motor spirit showed that the
upper limit was reached with 1.84 times the theoretical
amount of air, whilst the lower limit was between 0.4 and
0.5, and with alcohol mixtures the upper limits were of
the order of 1.5 and the lower 0.4.

Generally with all commercial motor fuels the superior

CARBURATION

limits of combustibility varied very little, and the lower
limits still less, except for pure benzene.

The latter fuel, as benzol, may therefore be expected to
have a somewhat wider explosive range than ordinary
motor spirit, as it can burn rather more air, and does not
fail to fire when the mixture is enriched to a greater degree
than petroleum spirit would permit. ^

The following tables of Sorel's experiments show the^
velocity and colour of the flame with various mixture
strengths, and the author has observed similar flame
colours in a suitable apparatus attached to the cylinde
of an experimental engine in Dr Watson's laboratory in'
South Kensington. In his engine the mixture strength
can be varied, also the point during combustion at whicl
the observation is made.

Table IX.-

-Petroleum

Spirit. ^^t

Quantity of Vapour

Ratio of Air

Maximum Ob-

carried by i litre of

Introduced to Air

served Velocity.

t? ^ m 0 fir c

Dry Air at io° C. and

necessary for

Metres per

x\.ciiictrK.o«

760 mm. Pressure.

Combustion.

Second.

0.038

2.19

0.00

Incombustible.

0.044

1.85

0.30

Slightly combustible.

0.048

1.76

0.88

Blue flame.

0.056

1.49

0.94

5> J>

0.061

1.35

1. 10

)) )J

0.075

I. II

>o.38

Blue and green flame.

0.079

1.08

0.56

Green flame.

0.082

1. 01

0-53

Green and red flame.

0. 1 0 1

0.83

0.05

Green flame.

0.122

0.68

0.00

Incombustible.

PUF

.E Benzene.

0.037

2.30

0.00

Incombustible.

0.046

1.94

I-I3

Blue flame.

0.050

1.86

1.30

)J 3J

0.057

1.63

1.29

J) 5)

0.085

1.09

1. 12

)» ?)

0.094

0.98

1.04

3) 33

0.104

0.89

Green flame.

0.124

0.76

0-53

Green and red flame.

0.2II

0.44

0.25

Red flame.

VELOCITY OF FLAME 23

Quantity of Air Required. — When considering the
amount of air required to form an explosive mixture, this
may be done in several ways, either as a ratio of weight
of air to weight of fuel, or as a ratio of the volumes of the
two substances, or as a proportion of air to saturated
vapour of the fuel. Care must therefore be taken to avoid
confusion. As a rough indication we may take, in round
figures, that the i vol. of petroleum spirit requires
10,000 vols, of air introduced through the carburettor to
give complete combustion. In another form we may state
that I lb. of liquid fuel requires approximately 15 lbs. of
air for its combustion reduced to atmospheric tempera-
ture and pressure.

Consumption figures for various engines and carburettor
arrangements show that this latter figure may vary from
1 1 to I as the richest limit, to 18 or 19 to i as the
weakest. The ratio of 18 to i, if properly carburetted, will
give the highest thermal efficiency combined with power
production.

A richer mixture will give a slight increase of power
in many carburettors, but at the expense of thermal
efficiency.

In order to find the correct proportion of air to fuel, the
equation representing combustion must be considered, and
Mr E. Scott Snell makes the following calculation in order
to give definite values for the various constituents of
petroleum spirit.

Combustion may be represented as taking place accord-
ing to the formula (for hexane) —

2.CgHjj + 1902= 12 COo-f- 14 HoO.

i.e., 2 vols, of vapour require 19 vols, of oxygen contained
in 19x4.81 =91.3 vols, of air ;

Or, 100 vols, of mixture contain 2.14 per cent, vapour.

By further calculation we can arrive at the following
table, showing the proportions for those members of
the petroleum group usually met with in automobile
practice : —

^m CARBURATION
Table X.

Fuel.

Formula.

Sp. Gr.

Ideal Mixture.

Pentane
Hexane
Heptane
Octane -
Nonane

QHl2

C7H16

^8"lS
^9 "^20

0.626 to 0.640
0.663 to 0.680
0.688 to 0.700

0.719

0.728 to 0.742

2.53 per cent.

2.14

1.86

1.64

1.46

It will be seen that as the specific gravity of the fuel
increases a greater proportion of air is required for combus-
tion. The proportions given are those required to give the
greatest explosive effort when the mixture is fired in a
confined space.

We will now proceed to make an elementary calcula-
tion to show how the correct amount of air can be arrived
at, knowing the chemical composition of the fuel.

Taking a Borneo spirit of 91 per cent, carbon and 9 per
cent, hydrogen, i lb. carbon requires 1 1.6 lbs. of air for its
complete combustion —

.". 0.91 X 11.6=10.5 lbs. of air for the C.

I lb. hydrogen requires 34.8 lbs. for its complete
combustion —

0.09 X 34.8 = 3. 14 lbs. of air for the H.

Hence, theoretically, the total air required = 13.64 lbs.,
which at 62° F. = 182 cub. ft. at atmospheric pressure.
In practice, we find the excess of air admitted greatly
dilutes this mixture, and that instead of a mixture con-
taining 1.8 per cent, of petrol vapour, the vapour is diluted
with 60 or 70 times its own volume of air, I'.e.^ the percentage
of petrol is only 1.6 or 1.43.

The investigations of Sir B. Redwood upon the limits
of explosion of mixtures of petrol vapour and air show
that when using a petrol of 0.720 sp. gr., and firing the
mixture in a closed vessel by means of a naked flame,

ibHI

THEORETICAL MIXTURES

the most explosive mixture consisted of 1.86 per cent,
of petrol vapour. With a petrol of 0.680 sp. gr. these
figures become 2.5 per cent., as is shown in the following
table :—

Table XL

Specific Gravity of Petrol 0.680, givinc. 190 to 260 Times its Own
Volume of Saturated Vapour.

No ignition with -
Silent burning with
Sharp explosion with
Violent explosion with -
Less violent explosion with
Burning and roaring
Burning silently

The most violent explosion occurred when 12.25 vols,
of liquid were mixed with 100,000 vols, of air.

These experiments were conducted without a previous )f\
compression of the mixture, and it is chiefly owing to this [
compression in an engine cylinder that such weak mixtures i
as are used in modern practice can be made to explode.

The following interesting figures are given by Eitner as
the proportions of various gases to air corresponding with
the explosive limits of the mixtures : —

Table XI L

1.075 per

cent, by volume of petrol vapour

1-345

2.017

2.352

3-362

4-034

5-379

Combustible Gas at 60° F.

Lower Explosive
Limit.

Upper Explosive
Limit.

Hydrogen . . _ .

9-45

66.40

Water gas - - . _

12.40

66.75

Acetylene . . . .

3-35

52-30

Coal gas -----

7.90

19.10

Methane -----

6.10

12.80

Benzene vapour

2.65

6.50

Benzoline vapour

2.40

4.90

Alcohol -----

8.00

12.00

Ether -----

2.00

8.00

Petrol -----

2.00

5.00

I 26 VH' CARBURATION IHH^^^^^I

I An insufficiency of fuel at the time of ignition will

I cause failure to ignite, but after the moment of ignition, air
I can be added to the burning mixture with satisfactory
I results, causing economy in working in some instances.
I The stationary engine made by the Westinghouse Brake
I. Co. works on this principle, and uses kerosene as its fuel,
i The Diesel engine also works with an excess of air, but its
I principle is different from that under discussion, as no
I sudden rise of temperature takes place.
1 ^ An excess of fuel, on the other hand, is generally due to

I lack of homogeneity in the mixture which the carburettor
\{ produces, and in order to eliminate weak zones in the
[\ mixture which might be adjacent to the ignition plug, the
I whole of the mixture is sometimes enriched so that its
I weakest zones are of normal constituency.
I It is essential that in a gas or vapour engine the working

\ fluid should be supplied to the engine in as homogeneous
a form as possible, in order that the rate of propagation of
the flame through the mixture may be uniform and of a
maximum velocity. Particularly is this necessary in high
speed engines, where the flame velocity has to be very great
in order that the pressure should, as it were, keep up with
the piston. It has been found in practice that where lack
of homogeneity in the mixture occurs, the expansion of the
burning gases is erratic, and produces humps on the ex-
pansion curve of the indicator card. Sometimes these
humps have been rather difficult to explain, but we may
take it for a fact that they are due to variations in the
stages of combustion of a liquid fuel due to the lack of
homogeneity in it. We do not find that these humps occur
in gas engine practice to any marked extent, and where
a hump has occurred it has been of a fairly regular forma-
tion, and may be due in some instances to the interchange
of heat between the burning mixture and the cylinder
walls. We find, however, in an engine burning liquid fuel,
that in some cases the hump is most marked, and one of
the points which the author raised in connection with a

HOMOGENEITY 27

recent discussion was that their regular formation on the
indicator card was probably due to the lack of homo-
geneity in the explosive mixture which was produced by
the particular carburettor fitted to the engine.

In further confirmation of this theory, it was pointed
out that the proportion of air to fuel was abnormally small
for a high-class carburettor under testing conditions, and
it is very probable that the mixture in this case was
too rich on account of lack of homogeneity. Certain
portions of the mixture were abnormally rich, in order
that the other portion of the mixture should have the
correct ratio of constituents in order to complete the
ignition.

It is difficult for our minds to consider the smallness of
a molecule, but in the limit we may take it that an ordinary
perfect gas is body divided into its finest possible particles.
In a hydrocarbon mixture, gas with air, it is obvious that
in order that the rapidity of the combustion should be
ensured, the hydrocarbon must be divided into the finest
possible particles, so that each molecule of hydrocarbon
can combine at the critical moment with its necessary
molecules of oxygen.

One of the objects of the carburettor is to break up the
fuel into these finely divided particles, in the limit, into a
gas or mist, and any variation from this idea is a step in
the downward direction in carburation.

We come, therefore, to the question of surface to volume
ratio, and it is a well-known fact that a sphere presents the
smallest surface to volume ratio of any known shape. Now
if one studies the formation which a liquid takes in issuing
from an orifice, or in moving through space or the atmos-
phere, one of course notices that the spherical form is
always taken by the particles. We have, therefore, as a
peculiarity of nature, to deal with liquid which naturally
presents to us the greatest difficulty with regard to its
presentation of surface for the carbu retting process. We
ought, therefore, to divide these globules into their largest

CARBURATION

number possible, in order to present a maximum surface of
fuel from which evaporation can take place. A simple law
of mathematics shows us that the relations between the
volumes of different bodies are to one another as the cubes
of their diameters, so that if we have a globule whose
diameter is i in any particular units, and another globule
whose diameter is 2, the latter will contain 8 times as
much matter as the former. The importance of fine sub-
division of the fuel in the carburettor itself is thus em-
phasised, as it is obvious that those particles of hydrocarbon
at the centre of a globule cannot combine with the oxygen
of the air until they are actually in contact with it. This
means that the time element is proportional to the size
of the globule, and where rapid carburation takes place,
either the subdivision of the fuel must be very fine, or an
excess of fuel must be permitted to pass through the
carburettor, the external portions of each globule only
being correctly mixed with its necessary amount of
oxygen.

In this latter case either the fuel passes as liquid into
the engine cylinders and is there burnt, causing distortions
of the true expansion curve, or it passes away unburnt to
the exhaust. It is the author's contention that heavy fuel
consumption is due to the lack of sufficient subdivision of
the particles of fuel in the carburettors themselves.
Furthermore, in many cases, although this subdivision
or spraying may take place in the first instance, its
effect is nullified by obstacles presented to its path
through the carburettor and inlet pipe on the way to the"
engine.

Such a state of affairs undoubtedly takes place when-
ever a change of direction in the flow-path occurs, and it
can only be minimised by the application of heat.

A controversial point here arises, as to whether it is
better to allow the mixture to enter the engine at practically
atmospheric temperature, thereby getting the greatest
weight of charge into the cylinders every time at full

IMPORTANCE OF SPRAYING

throttle opening, or to allow the mixture to reach a higher
temperature, at which it is perfectly carburetted, although
the weight per charge is less.

The author is certainly of opinion that the latter is the
better state of affairs, as although the weight of charge may
be slightly less (due to its rise of temperature), the more
homogeneous mixture in the latter case will burn far more
efficiently. By this is meant that the rate of propagation
of the flame through a homogeneous mixture is more rapid
and regular than is the case where the surface to volume
ratio of the incoming fuel varies from one location to
another.

Heat Required. — It has already been pointed out
that in order to change the state of a body from a
liquid to a gas, heat must be applied, and this in amount
must be equal to the latent heat or evaporation of the
fuel.

Let us consider first the lighter constituents of petroleum
spirit, say hexane, whose specific heat is 0.50, with a latent
heat of evaporation of 117 calories per kilogram.

This fraction is mixed with other heavier fractions, so
that probably the average latent heat of the whole of the
spirit is of the order of 160 calories per kilogram.

We will, therefore, consider a fuel whose latent heat is
160 calories per kilogram, and whose specific heat is 0.50,
and it is necessary to supply these 160 calories to every
kilogram of fuel vaporised, if the resulting temperature
of the mixture is to be the same as that of the surrounding
atmosphere.

If air heating is employed we must first take into
account the specific heat of the air, and that, as com-
pared with water, is 0.2375. In other words, 0.2375
of a thermal unit will raise the temperature of the air
through 1° in any scale whether English or C.G.S. units
are taken.

Supposing now that the theoretical quantity of air is

CARBURATION

supplied, i.e., fifteen times the weight of the fuel, or 15 kg.
per kilogram of fuel, we have as the result : —

Spirit, latent heat
Air, 15x0.2375

160

Total

0.50
3-56

4.06

The quotient — ^ = 394° C., as the rise in temperature of

the air entering the carburettor, i.e., 71° F.

If a lighter spirit, such as hexane, is used, these figures
become 28° C. or 50.5° F. Now the Table VIII. shown on
p. 19 shows that, say, heptane can only exist as vapour at
a temperature of 3.6° C, so we must add the value just
found, i.e., 394 + 3.6 = 43° C. should be the minimum initial
temperature of the air in order to effect complete vaporisa-
tion in the carburettor.

If the engine speed is higher, so that the fuel does
not have sufficient time to absorb the necessary heat in
the carburettor and induction pipe, the temperature of the
air should be higher.

We will now proceed to discuss how an excess of air,
when working, allows of a lower working temperature to
be maintained in a homogeneous mixture such as hexane.

This fraction, as seen in Table VIII. just referred to, will
remain in vapour form with the correct amount of air
at a temperature as low as — 17.7° C. (Sorel), and complete
evaporation would only remain possible if the initial
temperature of the air were 28— 17.7= 10.3° C.

If, however, about 1.3 times the theoretical amount of
air be present, or 19.9 kg. of air per kilogram of hexane,
the minimum temperature of saturation is — 24° C, and the
thermal capacity of the mixture of air and hexane is : —

Hexane, latent heat -
Air, 19.9x0.2375 -

0.50
4-73

Total

523

THE EFFECT OF HEAT 3 1

117

The temperature drop is, therefore, — ^ = 22.4° C, and the

minimum temperature for the incoming air is 22.4—24 =
-1.6° C

Now if we consider the temperatures at which mixtures
of heptane and air will remain stable, we find that for
a correct mixture the minimum temperature is 3.6° C,
but if the mixture is enriched with 20 per cent, of fuel,
the temperature can be reduced to practically zero C, i.e.^
32° F. The richer the mixture the lower the temperature,
but we may take it that at the freezing point of water we
have practically the limit at which a carburettor will work.

Now we come to the explanation of a fact which is
not generally understood, viz., why it is that a fixed
carburettor, or carburettor in which the relations between
the air-flow and the fuel-flow are pre-determined, does
not always work well until it is warmed up, and that it
is sometimes necessary to flood the carburettor before
the engine will start. This is entirely due to the complex
nature of the fuel, and to the absence of sufficient heat
supply to effect carburation. From the previous figures,
in which it was pointed out carburation would not remain
stable unless the mixture was abnormally rich, it will be
obvious that in order to obtain carburation, and maintain
it when the temperature is low, it is necessary to do one
of two things — either to make the mixture abnormally
rich or to ignore the heavier fractions of the fuel, and
carburate only with the lighter one, allowing the heavier
ones in the first instance to be carried through the engine
unconsumed.

It is often pointed out that the so-called automatic
carburettors are difficult tp start, and will not work until
properly warmed, and that it is absolutely essential for
their working that they be either water-jacketed or heat-
jacketed in some way. This is perfectly true, as if in a
properly designed carburettor of that type the fuel is
correctly proportioned for running under normal condi-

CARBURATION

tions, when the conditions are abnormal, the air supply
must be shut down or the fuel supply temporarily increased.
It may occur to the reader that there is one other way
of adding heat to effect carburation, viz., adding it to the
liquid before it is mixed with the air, but on considera-
tion it will be obvious that as the relative weight of liquid
to air is small, of the order of one to fifteen, that although
the specific heat of the liquid is very considerable as com-
pared with that of air, it would be impossible to add
sufficient heat to the liquid in order to supply the necessary
thermal units required for the latent heat of evaporation.
Now the specific heat of the liquid is only about three
times that of the air, and as there is about fifteen times
as much air as fuel by weight, it is quite obvious that
it would be necessary to raise the temperature of the
liquid through say five times the range that it is necessary
when dealing with the air. This is quite impossible, as
the lighter fractions of the fuel bec^in to come off at a
fairly low temperature. Some carburettors certainly dcfll'
heat the liquid fuel, but not to the extent here indicated ;
and furthermore, it must always be borne in mind that
in those types in which the fuel is heated there is another
effect, viz., that of reduction of the viscosity of the fuel, so
that a greater quantity passes through the same sized orifice
under similar conditions than would be the case were the
fuel used cold.

A hot-water jacket in a carburettor, in addition to
heating the fuel, does of course heat the incoming air, but
it has been found in modern practice that an extension of
the hot-water jacket is really necessary, and the jacket is
therefore carried a considerable distance along the induc-
tion pipe.

As showing the effect of temperature upon the viscosity
of a certain brand of motor spirit, the author's tests, made
some time ago, show the following times taken for a sample
quantity to pass through the instrument ; —

TEMPERATURE EFFECTS 33

Table XIII.— Effects of Temperature upon Viscosity.

Head over orifice = 60 mm.
Tests of sample quantity through instrument.

Fuel: "Anglo

Petroleum Distillate

0.760" Spirit.

between 1 50° and 300° C.

Temperature " F.

Time taken in seconds.

270

400

255

390

220

375

180

120

165

...

150

• • •

In the above table the sample was a volumetric one,
and not measured by weight, and it will be noticed that as
the temperature was raised the fuel became less viscous,
and a less period of time was occupied in passing through
the orifice.

Simultaneously with the decrease in viscosity we have
a decrease in specific gravity, which in other words
signifies that a less weight of fuel is contained in the
volumetric sample when hot than when cold.

If by any means one could arrange that the fuel passage
was so shaped with regard to its frictional properties that
these two variables coincided, then we should have a
flow of constant weight of fuel at all ordinary working
temperatures. This does not, however, occur in practice,
as when the orifice is of the usual shape the viscosity
decreases more rapidly than the specific gravity, so that
when the fuel is warm a greater weight passes through the
orifice in unit time than when the fuel is cold. This matter
is further discussed in Chapter V., dealing with the flow
of fuel through small orifices.

The following table shows the increase in the weight
of any one distillate that will pass through a small orifice,

CARBURATION

as its temperature is raised, and also the decrease in fuel-
flow as a distillate of a heavier specific gravity is sub-
stituted.

It will also be noticed that it is not really necessary
to increase the size of the air aperture when using a heavier
fuel, as the viscosity of that fuel retards its rate of flow.*

Table XIV. — The Weight in Grammes of Various Distil-
lates FLOWINCx THROUGH A LONG TUBE OF SmALL DiA-

meter under the same Pressure.

Petrol.
Sp. Gr.

0.700
0.725

0-755

Boiling Point.
Deg. Cent.

Temperature Degrees Centigrade.

12-134

70-134
125-196

125-5
90
68.5

128.5
97-6
71-5

131-5
104

J 34. 5
III

79-5

This matter is discussed more fully and the table
amplified in Chapter V.

Table XV. — Viscosity- = >/ (Watson).

Viscosity in C.G.S. units

dyne sec.

Fuel.

Density at
15° C.

cm.-

5°C.

15° c.

25° c.

0.00332

Bowley's special

0.684

0.00380

0.00352

Carless -

0.704

0 00406

0.00380

0.00359

Express -

0.707

0.00445

0.00420

0.00398

Pratt

0.719

0.00445

0.00420

0.00398

Carburine

0.720

0.00450

0.00421

0.00400

Shell -

0.721

0.00454

0.00421

0.00400

Benzol -

0.846

0.00609

0.00572

0.00539

0.760 Shell

0.767

0.00534

0.00498

0.00472

Hexane -

0.680

0.00376

0.00342

0.00319

* It is interesting to con

ipare these r(

isults with those of the sa

me authority

on p. 53.

VISCOSITY VALUES

The weight of a h'quid of density D which flows on
/ seconds through a tube of radius r cm. and length
/ cm., when the length is great as compared with the
diameter.

H = the head in cm. of the liquid over the orifice.

>/ = the viscosity of the liquid.

^=the acceleration of gravity = 981 cm. per sec. per sec.

W = the weight of the liquid in grammes.

8/77 '

The author's figures for variation in the specific gravity
due to a rise in temperature of the liquid are as follows : —

Table

XVI. — Fuel Tested: "Anglo

0.760."

Temperature
in ° F.

Specific
Gravity.

Temperature
in°F.

Specific
Gravity.

54 .-

60 - -

- 0.732

- 0.730

81 -
86 -

- 0.720

- 0.718

65 -. -

- 0.728

90 -

- 0.715

70 -

- 0.725

95 -

- 0.713

75 -

- 0.723

Theor

ETICAL.

100 -

- 0.710

120 -

- 0.700

no -

- 0.705

130 -

- 0.695

It will be seen that the decrease in the specific gravity
is not very material, and would in itself only tend to
increase the head of petrol by allowing the float to sink
deeper into the liquid, retarding its action on the valve
which it controls. This retardation means that the petrol
would stand at a slightly higher level in the jet, and,
in cases where the petrol level is set high, it might cause
flooding.

CHAPTER IV

mLET PIPES AND INERTIA

We will first set down the definition of the word " inertia "
so that we may be quite clear upon this point. Inertia is
that property of a body by virtue of which it tends to
continue in a state of rest or motion, in which it may be
placed, until acted on by some force.

Of all the details of a motor car engine, the carburettor
and the carburetting system is most sensitive to the
question of inertia, for the reason that conditions are
continually and rapidly changing, and that the masses of
air and fuel which are dealt with are subject to inertia the
whole time during which the engine is working. Were
an engine working at a constant load and speed throughout
the whole time, the question of inertia would not come in,
but as this is not the case, we will briefly consider the
effect of inertia, both of the air and fuel, and of the moving
parts where an automatic carburettor is concerned.

Newton's second law of motion states that " Uniform
acceleration is produced by any constant force, the latter
being measured by the increase of momentum it produces."

The force producing an acceleration = — x F, where w is

the weight of the body, g is the acceleration of gravity, and
F the acceleration produced.

The final velocity of the body v = Fx/, where ^=the
time during which the acceleration acts.

Every body has an inherent quality or inertia by
which it tends to resist a change of velocity, and the

kinetic energy of such a body in motion = , where M is the

mass of the body.

THE PROPERTIES OF AIR

When we compare, firstly, the masses and weights of the
two bodies, petroleum spirit and air, we find that a cubic
foot of spirit weighs, say, 45 lbs. if its specific gravity is
0.720, and that a cubic foot of air weighs as follows : —

Table XVII. — The Properties of Air.

Vohime at Atmospheric Pressure.

Temperature,
Fahrenheit.

Density in Pounds

per Cubic Foot at

Atmospheric Pressure.

Cubic Feet per

Comparative

Pound.

Volume.

11.583

0.881

0.0863

12.387

0.943

0.0807

12.587

0.958

0.0794

12.840

0.977

0.0778

13.141

1. 000

0.0761

13-342

1. 015

0.0749

13-593

1.034

0.0735

13-845

1.054

0.0722

100

14.096

1.073

0.0709

1 10

14-344

1.092

0.0697

120

14.592

I. Ill

0.0685

130

14.846

1. 130

0.0673

140

15.100

1. 149

0.0662

150

15-35J

1.168

0.0651

160

15-603

1. 187

0.0640

Air expands ^J-y of its volume at 32° F. for every
increase in temperature of 1° F., and its volume varies
inversely as the pressure.

The volume of i lb. of air at 32° F. = 12.387 cub. ft., and
at any other temperature and pressure its weight in pounds
per cubic foot

^y_ 1.325 XB

459.2 +t'

where B = the height of the barometer in inches of mercury.
T = temperature in degrees F.
1.325 = the weight in pounds of 459.2 cub. ft. of air at 0° F.
and one inch barometric pressure.

38 CARBURATION

We find, therefore, that the ratio of the mass of a aTRic

foot of fuel to that of air is of the order of — ^ — = ^5^

0.0807

times as great.

The smaller the quantity of fuel acted upon by a change
of engine suction the smaller will be the inertia, but the
velocity of the stream is of great importance, as the
momentum varies as the square of that velocity.

For these reasons it is advisable to have the orifice in
the jet tube of as little capacity as possible, and to keep
the velocity of the fuel through that passage low in cases
where inertia effects are likely to be of moment.

In a carburettor system only small quantities of fuel
and air are acted upon, and the dimensions of the orifices
can be so arranged that inertia factors scarcely come into
consideration except at slow engine speeds.

So far as the air is concerned, the effect of lag of flow
on account of inertia is shown by Fig. 2 ; but the lag of
fuel-flow may be more pronounced, thus giving a weak
mixture at first, to be followed by a rich mixture when
the air-flow is retarded. The air enters the mixing
chamber more readily than the fuel, but when the throttle
is closed there is always the tendency for the fuel to con-
tinue flowing unless a suitable damping device is employed.

It is, however, possible to design the passages of such
small dimensions, and to arrange the friction of the orifices
to be so high, that inertia can almost be damped out.
High jet friction is, therefore, one of the means of counter-
acting the inertia of the fuel, and this can be arrived at by
making fuel orifices many in number, by giving either a
very small unobstructed hole for the fuel supply, or a hole
of larger dimensions in which some medium is interposed
for producing high jet friction.

The author has had the opportunity of discussing the
question of inertia with Mr A. G. Jonides, the designer of
the Polyrhoe carburettor, whose opinion upon the subject
is as follows : —

LAG OF FLOW

" When the throttle is closed there is a steady, or nearly-
steady, flow through the carburettor. Under this condition
a certain ratio of jet area to choke area may give what is
wanted. If now the throttle be opened, with the engine
loaded to run slowly, the flow through the throat of the
carburettor becomes fluctuating. The velocity of the air

lovides Curve

ofFtt

rol Di

scharc

ed fje^ Secohd
Or Hick ■ '01575 cms

i^'04d;

■

area

•OOO0:

10, cm

1^*

• 1^

§ -2

f<ft

\y^

5 ^*

-^^

iO ZO 30 40 SO 60 70 SO 90 /OG

Cenhmelres Head

Fic. I. — lonides' Curve.

past the jet orifices varies more or less as the velocity of
the pistons in the engine. That is to say, the curve of
velocities is roughly a sine curve, rising and falling har-
monically. So much for the air. Now, does the velocity
of the fuel vary in the same way ? It ought to if constancy
of gas is to be retained. But the fuel has weight, and even
at moderate engine speeds it tends to continue flowing

CAPBURATION

when once it has been set in motion. The result of this
inertia is that the velocity of the fuel does not fall off as
rapidly as the velocity of the air. Hence there is an
excess of fuel. At higher speed this excess is naturally
greater. To use an electrical term, the current of fuel
'lags' behind the current of air, just as in a circuit carry-
ing an alternating current of electricity, and having inertia
as well as resistance, the current lags behind the pressure.
In the simplest case, that of true harmonic motion, the
amount of lag can be defined as * the angle between

Pressure in Inlet Pipe during Induction Stroke.

^^\

...

to
o

- /

\n
o

„

,_^

3
o

. ■^'i-aJ

, ^

^ -,

•V

30*

60°

90* 120"

Crank- Angle

150*

(80«

aio"

Fig. 2. — Inlet Pipe Pressure.

two points on a circle whose movement round that circle
would give that lag.' In an electrical circuit, the tangent
of the angle of lag is equal to 2?^ times the inertia (o
inductance) of the circuit divided by the resistance.

" The inertia of the fuel can be calculated easily. The^
resistance has to be approximated, because for any practic-
able jet there is no true analogue to electrical resistance.
The friction in a jet appears to be something between an
electrical resistance, in its behaviour, and a function of the
velocity of the flow.

" Still a sufficiently close approximation can be made,
and a jet designed to have a resistance sufficiently high

lONIDES THEORY 4I

and an inertia low enough to reduce the angular lag to a
few degrees only at the highest practicable engine speed.

" Such a jet is used on the Polyrhoe. On an engine
with automatic inlet valves — a condition, it is true, which
favours the experiment — the absence of any material lag
was fully demonstrated. The open throat of the carburet-
tor was illuminated by a vacuum tube lighted through a
contact on the half-time shaft. As this contact was rocked
to light the carburettor at different phases in the cycle, the
throat could be seen either full of spray or quite empty as
though the carburettor were not at work."

The question of jet friction plays a large part, as may
be supposed, in the question of the inertia, but this may
also be accompanied by the phenomenon of capillarity,
being the tendency for a liquid to creep up a small orifice
in a contrary direction to that which it would normally
assume under the action of gravity. Capillarity often
causes a carburettor to leak by reason of the liquid either
creeping up through the jet or creeping up the stem of the
valve which, at its lower end, dips into a fuel reservoir, and
this action has caused considerable trouble in certain types
of carburettors.

Passing from the carburettor now to the inlet pipe,
inertia plays a very important part in the design of inlet
pipes for all types of engines, whether they be of the single- 1
cylinder or of the multi-cylinder pattern. When we con-
sider a four-cylinder engine firing on the usual system,
namely i, 3, 4, 2, turbulence is set up in the inlet manifold,
and this turbulence is further aggravated by the inertia of
the explosive mixture passing through that manifold. In
such a type of pipe, particularly if the ends terminate
abruptly, there is always the tendency for the fuel to load
up the outer ends of the pipe by reason of the two cylinders
in one pipe firing in sequence, and then the two cylinders
on the other pipe. The gas flows rapidly, first towards one
end of the pipe and then towards the other, and the gas-
flow lags behind the cylinder demand, so that when the

CARBURATION

inlet valve of either end cylinder is suddenly closed, the
gas continues to flow down the pipe and banks up with
increased richness at the two ends. Considerable difficulty
has been experienced, particularly in the older patterns of
engines, by reason of the end cylinders getting a different
consistency of charge from that which is supplied to the
middle pair of cylinders. In special designs of inlet pipes
for racing cars, great care is often taken to overcome the
inertia of the mixture in the pipe, and a continual flow-
path is given to the gases by means of either figure-of-eight
inlet pipes or circular pipes, so that the gas-flow is constant
and unidirectional the whole time.

Rapid closing of the inlet valves also sets up a wave
motion in the inlet pipe, and there are possibly conditions
under which wave motions, thus set up, may synchronise,
causing difficult conditions to occur. It is better if such
waves of pressure damp each other out before reaching the
carburettor, or are allowed to dissipate themselves in a
chamber within the water jacket. The provision of such a
chamber is referred to in connection with another phase
of carburation, but it also applies here. We know for
a fact that certain critical lengths of inlet pipes exist
in practice, and one is often asked to explain why the
lengthening or shortening of a certain pipe has led to
improved results.

The explanation is that there is probably some critical
wave length in the pipe in question at certain engine
speeds which causes great fluctuations of pressure.

Another effect of the inertia of the incoming mixture is
that at the moment of inlet valve opening, unless there is
a considerable negative pressure, or pressure below that of
the atmosphere in the cylinder at the time of valve opening,
the explosive mixture hesitates before entry into the
cylinders, and it is only when the acceleration of the piston
puts a more or less sudden increase of suction upon the
mixture that the mixture itself follows in behind the piston.
It may occur in some engines that a negative pressure of

PULSATIONS AND TURBULENCE 43

as much as 5 lbs. per square inch is momentarily produced
somewhere about half-piston stroke, or rather later, before
the inertia of the explosive mixture is overcome. After
this time the mixture rapidly follows up the piston, and
advantage can then be taken of the inertia by retaining the
inlet valve open for some considerable time after the outer
dead centre has been reached.

American practice generally retains the inlet valve open
later than European practice. Some American designers
retain this valve open for 40' after the outward dead
centre has been reached. In European practice, however,
such a late closing of the inlet valve is seldom found, and
this is probably due to the fact that in Europe the valves
are of larger diameter.

From the figure previously given, it will be evident that
the inertia has a considerable effect upon the carburettor
action by reason of pulsations being set up in the inlet
pipe, due to the suction which is necessary to overcome the
tendency to lag, but in a high speed engine these variations
usually balance out. Whether they do or do not depends
on the length and design of the inlet pipe.

A theory has been propounded that there is a consider-
able surging effect in the inlet pipe of the majority of
engines. This surging undoubtedly occurs at low speed, as
has been observed in several types of carburettors where it
has been shown that at certain periods the suction decreases
altogether, and the inertia of the gases in the reverse
direction, after the moment of valve closing, causes the fuel
to blow back out of the air orifice of the carburettor.

With the modern perfection in carburettor design, it
is very often probable that as the mixture leaves the
carburettor it is fairly homogeneous, but owing to the
pulsations taking place in the inlet manifold, the mixture
as it reaches the various engine cylinders may vary
considerably in richness. At the carburettor outlet the
succession of engine impulses will produce a fairly uniform
flow of carburetted air, but this can scarcely be said to be

CARBURATION

true in the manifold itself. Owing to the inertia of the
gases along the pipe, there is always a tendency for the
heavier particles of petrol vapour to drive towards the ends
of the pipe, causing very slight and instantaneous variations
of pressure in the mixture.

Certain periods in the working of an engine must occur
when the pulsations of the mixture in the inlet pipe
synchronise with the periodicity of the pipe itself, thus
tending to upset the carburation to certain engine cylinders.
Under these conditions pressure waves are set up, due to
the impulses of the mixture on its way to the various
cylinders, and for this reason it is necessary, in special
cases where carburation is of very great importance, to
keep the mixture flowing in one direction only, and n
allow reversals of flow in the mixture stream to occur.

It is noteworthy that considerable improvements in
carburation, particularly with six-cylinder engines, have
been made by eliminating the induction pipe entirely, and
coring the inlet passages within the cylinder casings. This
may be accountable for by two reasons, one being that
heat is added to the mixture during its rapid circuit from
the carburettor to the engine ; and the other being, that
the passages cored through the engine itself are generally
of considerable magnitude, so that the surging flow is
thereby much reduced.

There is no doubt that if an inlet pipe be made of
sufficient size, and that enough heat is supplied to it to
prevent condensation of the vapour in the pipe, local varia-
tions of pressure will be reduced to a minimum. In one
particular case of a six-cylinder engine which had been
difficult to carburate with a certain type of carburettor,
the re-design of this engine, with the inlet pipe eliminated
and the incoming charge carried through cored passages,
entirely overcame the previous carburettor difficulty.

The modern tendency to place not only the induction
manifold but also the mixing chamber within the cylinder
water jackets undoubtedly tends to improve carburation,

INLET PIPE DESIGN 45

by reason of the facilities such an arrangement gives for
suitably heating the fuel vapour.

It has been an axiom in the past that the area of the
inlet pipe between the carburettor and the valves should
not undergo any great change in dimensions, on account
of the drop in velocity aggravating precipitation. In
modern practice, however, when a drop in velocity is
permitted, and hot walls are presented, any liquefaction
of vapour or precipitation of suspended particles is suitably
Inet by hot surfaces.

When the percentage of heavier fractions in the fuel is
high, any temperature obtained in the water jackets is in-
sufficient to evaporate such fractions when precipitated, as
such temperature is below ioo° C. High velocity must,
therefore, be resorted to, in order to maintain such particles
of fuel in suspension.

Furthermore, a manifold of considerable capacity tends
to damp out all those pressure variations previously
referred to, and equalise out the suction at the carburettor
jet.

Reverting again to the question of inertia, and the
difference between that of the fuel and that of the air in a
carburettor system, we must not confuse the vapour with
the liquid fuel. If all the fuel is vaporised in the carburettor
and properly mixed with the air, although the vapour
density is about three times that of the air, the maximum
variation in the volume of fuel vapour is only between
1.2 and 3.2 per cent. (Dr Watson) of the volume of the
air. However, if the fuel is only partly vaporised, fuel is
carried in suspension, and it is from these suspended liquid
particles that difficulties occur.

Dr Watson, in his experiments upon a four-cylinder
four-cycle motor, made some interesting indicator measure-
ments of the pressures in the induction pipe at different
speeds of engine rotation. He showed that at a speed of
656 revs, per min. the pressure at the moment of inlet
valve opening, i.e., 20° late, was slightly above atmospheric,

CARBURATION

and continued to rise even after the valve had opened, due
to the inertia of the mixture in the pipe. As soon as the
valve opened appreciably, i.e., at a crank angle of 45°, the
pressure fell to atmospheric, and rapidly dropped to a
minimum of — 1.3 lbs. per square inch, where it continued
until at 150° crank angle it was at — I lb. per square inch.
At the moment of valve closing, i.e., at a crank angle of
200°, or 20° late, the pressure had risen to slightly above
atmospheric.

When the engine speed increased to 860 revs, per min.
the pressure at valve opening was down to —0.4 lb. per
square inch, with a maximum depression of — 1.8 lbs. per
square inch, and rising to —0.3 lb. per square inch at valve
closing.

At a speed of 1,200 revs, per mjn. the corresponding
pressures were — 1.2 lbs. per square inch at valve opening ;
maximum depression, —2.3 lbs. per square inch; and
— 1.2 lbs. per square inch at valve closing.

From the following table it will be seen that the
pressure in the induction pipe at the moment of valve
closing is above the mean pressure : —

Table XVIII.

Speed Revolu-
tions per Minute.

Mean Pressure,

Lbs. per Square

Inch Gauge.

Pressure (Gauge) at
Moment of Valve Closure,
Lbs. per Square Inch.

656

860
1,200

-0.9
- 1.2

-1-7

+ 0.1
-0.4
- 1.2

This engine can scarcely be taken as an example of
modern design, on account of the apparent smallness of its
valves which have caused the wire drawing.

The area through the carburettor was also probably a
good deal less than would be the custom in modern
practice, where a sufficient area is provided to permit

PRESSURE IN INLET PIPES 47

engines to attain speeds of 2,500 revs, per min. in
normal working.

In Dr Watson's engine the volumetric efficiency varied
from 78 per cent, at 500 revs, per min. to 63 per cent, at
1,300 revs, per min., which can scarcely be considered good.
These values could easily be brought up to 90 per cent, at
the lower speed, and 80 per cent, at the higher, by suitable
design.

A useful formula for measuring the weight of air
passing through a circular opening is as follows : —

w = aF/ ojlpp.

Where w = the weight of air in lbs. or grm.

F = the area of the hole in sq. ft. or sq. cm.

/o = the density of the air in lbs. per cub. ft. or cub.

cm.
a = the coefficient of contraction of the orifice = about

0.597-
/ = the time in seconds.

/ = the pressure difference in lbs. per sq. ft.

CHAPTER V

THE FLOW OF FUEL THROUGH SMALL ORIFLCES

The subject of the following few chapters has been one to
which the author has given particular attention, and in the
absence of authoritative matter from an engineering point
of view, dealing with very small orifices, no system of units
has become standardised for this purpose.

Some explanation, therefore, is due with regard to the
units adopted, and the reasons why the author has presented
the matter in this form.

The linear dimensions of the apparatus are most con-
veniently expressed in millimetres, as this unit of length is
particularly suitable for small work. The unit of volume
would be preferably expressed in litres or cubic centi-
metres, and scientifically this unit should be adopted for
the liquid. Swept volume of an engine is taken wherever
possible in cubic centimetres, as this volume is obtained
directly from linear measurement and calculation. Where
relations exist between swept volume and fuel consumption
for the purpose of calculation, the cubic centimetre is
adopted as the unit.

This book, however, is not solely written for the purpose
of scientific investigation, but is also for the practical
application by the motorist. Fuel is sold at present in
England by the Imperial gallon, and abroad by the
American gallon, or the litre, and for this reason, where
ready practical application of the data is possible, the
Imperial gallon is taken as the volumetric unit for fuel

The unit of pressure is a somewhat difficult one in a
carburettor system, on account of its small magnitude, and
the author has adopted that unit which is usually employed
in connection with fan work, namely, the inch of water
head. This is more convenient than the inch of mercury,

kU LI Ktj factors 49

as a water manometer is simple to construct, and the
medium under observation can be readily obtained.

Fractions of a pound per square inch or grammes per
square centimetre might lead to some complication, and
it must be distinctly understood that where the term
" inches of water head " is used it is merely an indication
of difference of pressure, and has nothing whatever to do
with water or petrol or any other fuel, and it does not,
therefore, apply in the hydraulic sense as representing the
head of the fuel over the orifice.

In discussing the control of fuel through an orifice by
means of some tapered pin device, it has been suggested
to the author by Mr A. S. E. Ackermann, A.M.I.C.E., that
the use of the word " modulating," as applied to the pin,
really expresses the function of this pin better than any
other word in common use, and a module is a thoroughly
well-known appliance, having existed for many centuries.

The ruling factors in the determination of the quantity
of liquid fuel which will flow through a carburettor jet
orifice are : —

(a) The viscosity of the fuel.

(J?) The temperature of the fuel.

{c) The shape of the orifice.

{d) The effective head actuating at the orifice.

With reference to the first two, these bear a certain
relation to one another, as the higher the temperature the
lower will be the viscosity of the fuel, and the greater
volume will flow through a small orifice in unit time as
the temperature is increased.

If, therefore, in motor car practice radiation or conduc-
tion of heat from the engine is allowed to influence the
float chamber and the liquid contained therein, an increase
of fuel supply will result as the engine warms up.

If regulation is perfect before the engine has reached
working conditions of temperature, the mixture will be too
rich in running, and, conversely, difficulties may be ex-

CARBURATiON

perienced until working temperature is arrived at with an'
instrument which is non-adjustable.

Broadly speaking, therefore, where efficiency is to be
maintained at all times, a fuel adjustment which will be
proportionately progressive from minimum to maximum
opening of the fuel and air orifices is essential.

Dealing, in the first instance, with the important
question of the viscosity of fuels at different temperatures,
the author some years ago conducted a series of experi-
ments to ascertain the effect of a rise of temperature of
the fuel in the Claudel carburettor. It will be remembered
that this instrument is provided with a water-jacketed base,
so that the fuel itself is heated on its way to the jet orifice.

For the purpose of these tests the author used a glass
instrument of the double sphere type having a constricted
opening between the upper and lower sphere. The whole
instrument was immersed in a water bath, and the tem-
perature noted. The ' following table gives the time in
seconds for the measured quantity of fuel to pass through
the constriction. Two fuels only are given, the ordinary
commercial motor spirit and a heavier distillate, between
150'' C. and 300° C.

Table XIX.*— Fuel : "Anglo 0.760" Spirit.

Effects of temperature upon viscosity. Head over orifice = 60 nwi.

Tests of sample quantity through instrument.

Fuel : "Anglo 0.760 "

Petroleum Distillate

Spirit.

between 1 50° and 300° C.

Temperature " F.

Time taken in seconds.

270

400

255

390

220

375

180

120

165

;;; ■»

135

150

* This is a duplicate of Table XIII., and is here inserted for the con-
venience of the reader.

EFFECT OF TEMPERATURE UPON RATE OF FLOW 5 1

At the same time the specific gravity of the fuel was
taken at different temperatures, and the values are given
in the following table : —

Table XX.* — Temperatures and Specific Gravities.
Fuel Tested: ^^ Anglo 0.760."

Temperature

Specific

Temperature

Specific

in " F.

Gravity.

in °

Gravity.

54 -

- 0-732

- 0.720

60 -

- 0.730

- 0.718

65 - -

- 0.728

- 0.715

70 -

- 0.725

- 0.713

75 -

. 0.723

Theo>

'etical.

100 -

- 0.710

120

- 0.700

no -

- 0.705

130

- 0.695

The above table indicates that there was a reduction of
approximately 0.005 in the specific gravity per 10" F. rise
in temperature.

Now we will proceed to deduce from the above two
tables what is the net effect of heating the fuel. For
example, we find that at 60° F. the specific gravity is 0.730,
and at 90^ F. it is 0.715, and at approximately the same
temperature, 58" F., the time for unit volume to flow is
270 sees., and at 90° F. the time is 220 sees.

We may say that in one second the relative number of
heat units passing through the orifice is proportional to the
specific gravities of the fuels at those temperatures. We
therefore have, taking the specific gravity of water at
1,000: —

At 60° F. 7^° = 2.7,

270

° T? 71 S

at 90 I*. - "^ = 3.24,
220

and the ratio ^^ =1.2;

2.7

* This is a duplicate of Table XVI., and is here inserted for the con-
venience of the reader.

CARRURATION

which means there is an increase of 20 per cent, in flow of
fuel as far as thermal units per unit time are concerned
when the temperature is raised from 60° to 90° F.

Let us compare these figures with those obtained
by Sorel, who experimented with a tube 49 cm. in
length, with a fuel head of 30 mm., the average diameter
of the tube being 0.775 n^^- These experiments were
more extensive and exact than those of the author, so
that the values can be depended upon under the conditions
prevailing, but it must be borne in mind that a long tube
and a fuel nozzle are different in their behaviour.

Referring to Sorel's data, fuel No. 6, a petroleum
distillate of sp. gr. 0.700, boiling between 12° C.
and 134' C, and taking the time of flow as constant,
measuring the weight of fuel flowing through the tube
at different temperatures, the specific gravity is there-
fore eliminated. We see that at 15° C, say 60" F., and at
32. 5"" C, say 90° F., the following weight of grammes passed

through the tube :-

15° €. = 72.5 grm.
32.5° €. = 78.5 grm.

J 72.5

That is, when the fuel was heated and passed through a
lon^ tube of small diameter its increase of flow was 8 per
cent, when the fuel was of low density.

As the density of the fuel is increased, the rate of
discharge at a higher temperature rapidly increases, as
compared with the rate of discharge when the temperature
is low. Between the same limit of temperature Sorel's
results show that with a fuel of 0.755 sp. gr. the increase in
the flow of fuel is 18 per cent., which agrees very well with
the figures obtained by the author.

The following table is taken from Sorel's book, p. 163,
and is of some importance at the present time, dealing
as it does with different fuels : —

THE FUNCTIONS OF A JET ORIFICE

w
w ^

PQ O
ID C/2

pi!
<

■■^
Pu
<

a
o
;^
o

O
?

Q
B

C/3

;:>
o

p<
>

W
H

:^
O

Q
<;
W

H
O CO

H
P

X p

10 0

• * vd 00 to

OnVO

• t^ Tj- N

H-i N

• • d vo to

00 10

• • r^ Tt M

«^

vo N t^ PJ

t^vO

vd d vo N ^

vo tT

OvOO vo ^ N

r^ vo

r- t^ r>. vo N

S-i

to On

dvvo M dv dv

vo ro

-^t

00 t>-vO to hH

vo vo

0 to

rf tOOO vd !>•

Tf ro

0
0

00 t^ vo to M

t^ vo Ov

d\co

0 dv Tj- Ti- vo

W N

00 VO VO to M

to vo to

>i^

VO VO

•<
u

t^VO M H-l •<t

M M

t^vo vo to •-<

l-l

0
vo

vo vo

to
06

vq
vo

?;
^

r^ tooO

vo to I>.00 to

0 N

t-- VO -^ N HI

00 r^ N f^

S-i

H- 6

-^ dv "4 vo HH

o\ c^

r^ vo r}- M t-i

vo vo vo N

0 t4

<
Ci::

t«i VO N »-< d

00 l-H

t^ vo ■«f N HH i

vo vo vovO VO

N -^

c«

d t< M ovod

l-l

rf M

r*. 10 rf i-<

tOOO vo vo

•

r-i

>■»

t-^

t/5

00 00 <j^^ t>.

vo -t to HH

00000

' ^

^ ^0 0 0

^ to to On vo 1-

}-i

rt M »-i i-H C4 rr>

•!->

:= 0 r :: :; :;

^00000

W N 0 vovO 0

M t^ N 0> vo

•-I M M

i-
(J
9

^ 0

-^1

-1

Wate

Pure

ale

c 0

0 lo vooo r^

0^-^

k: 0 M vooo >-i

Q t^ r-^ r^ t^oo

fiH

fl.

• 6666b

M t<

in -

vo r^OO Ov 0

CARBURATION

As a supplement to this table a few figures obtained by
the author, using Claudel jets, with a constriction 5 mm.
long in every case, may be of interest.

Table XXII. — Times taken for 60 c.c. of Liquid Fuel at
55° F. TO Flow through an Orifice 0.95 mm. Diametei

Fuel.

Specific
Gravity.

Head over Orifice in mm.

"Anglo 0.760" -
Distillate from paraffin
Benzol

0.730

0-795
0.88s

sec.

77
165
105

sec.
70
142

sec.

7*6

The Jet. — A carburettor jet has two functions to per-
form— first, that of spraying the fuel into the mixing
chamber, and second, that of regulating the amount of fuel
passing through the carburettor in unit time. We have
already dealt with the question of spraying, and we
now proceed to discuss how different types and forms of
jets can be designed and arranged to carry out the
measuring operations. It is a matter of history that a
jet was not at first employed, as the surface carburettor
was not provided with a jet. With the advent of the
Maybach instrument the jet came into use, and is now
almost universally adopted.

The modern carburettor designer does not by any means
hold to one particular type of jet, such as the circular orifice
or drilled hole which was the pioneer. We now have the
annulus and the slit, which may be variable in opening ; also
combinations of the two. Special forms of jet are now
very much in vogue, whose object is to control the flow of
fuel without the assistance of extra air devices.

We will briefly consider the conditions under which a
fuel jet has to work in ordinary practice, and it is quite
conceivable that, owing to the road resistance being high,

RELATIONS BETWEEN PRESSURE AND DISCHARGE 55

an engine may rotate at a slow speed with the throttle wide
open. Subsequently the engine speed may increase, and
the throttle closed down when the resistance diminishes.
During both these periods the power developed by the
engine may be the same, but, owing to some peculiarity
of carburettor design, the depression in the vicinity of the
jet may vary under these two conditions of working.

At the higher engine demands we may also find the

3
C/3

Fig. 3. — Revs, per Min. of Engine — One Unit= 100 Revs, per Min.

carburettor opened out to its maximum capacity and the
engine speed gradually increasing. The suction acting
upon the jet also increases, and causes a greater efflux of
fuel, and it is the duty of the jet to so proportion the fuel-
flow to air-flow that the mixture shall remain of constant
composition at all times.

We may have an instance where the throttle is close to
the jet, and closes the air-flow around it when the engine
demand is small — the suction is thus increased at the jet

CARBURATION

orifice. But in the first example we find the same small
demand with wide-open throttle and low engine suction.
The driver of a modern car does not consider these con-
ditions, hoping that by opening up his throttle the engine
power will respond at all times.

It is unnecessary to point out that at low air velocities
a jet device behaves erratically, as this has already been
shown graphically and otherwise by the author and others
from time to time. In order to get over these difficulties
there are two alternatives, one being the system already
described of concentrating the air-flow round the jet at low
engine speeds, and the other being to provide a separate
jet for slow running.

The Passage of Petrol through a Single Orifice. —
The object of the experiments contained in this series was
to obtain some practical data for the use of the motoring
world at large, as distinct from purely theoretical
deductions.

The test apparatus consisted of a small brass tank,
having a tube fixed into the bottom, which terminated at
the other end in a tee-piece. Into this tee-piece jet tubes
were screwed in turn, each orifice having been carefully
drilled to an accuracy limit of the stated diameters, the
maximum error being yj^ mm. The orifices used in the
experiments ranged -from 0.95 mm. to 1.40 mm. diameter.
The head of the liquid was varied within wide limits.

For the first series, pressure heads between 30 mm. and
90 mm. were taken in order to ascertain the probable
friction in the tube at low speeds of the fuel, but with the
30 mm. heads less liquid passed through than would be the
case in actual practice, except under conditions of no load
or very light load. The 90 mm. head corresponds to the
suction when the car is running on a level with the
throttle very slightly open.

In carrying out these experiments the fuel in the tank
was kept at a constant level, and the time noted in which
a given quantity of fuel passed through the orifice in the

FLOW THROUGH CIRCULAR ORIFICES

jet tube. This was done for heads of 30, 60, and 90 mm.
and upwards with each size of jet, and the appended Table
XXIII. shows the quantity of fuel which passed through the
orifice in gallons per hour, and the time taken in seconds
for the sample quantity. Intermediate values have been
filled in from the curves produced experimentally, and
the values have been cross checked, assuming that the
flow has been proportional to the area of the jet (or to
d'^) and to the square root of the head = //.

Table XXIII. — Claudel Hoeson Carburettor.
Jets Open-Ended.

Quantity

Time taken

Quantity

Time taken

Dia-

Head

Flowing in

for Unit

Dia-

Head

Flowing in

for Unit

meter of

Gallons per

Quantity

meter ol

Gallons per

Quantity

Orifice

Fuel

Hour =

to Flow =

Orifice

Fuel

Hour =

to Flow =

in mm.

in
mm.

Q=^;.

^_ 3600
80 xQ"

in mm.

in
mm.

Q.«

f- 3600
80 xQ*

sees.

0.95

0.32

140

1.20

0.515

»>

0.454

0.725

0.562

0.895

120

0.645

120

1.03

j»

ISO

0.725

150

1.16

1. 00

0.352

127

1.25

0.56

5»

0.51

0.786

0.62

0.97

120

0.715

120

1,116

150

0.805

5 J

150

1.25

1.05

0.392

114

1.30

0.608

>»

0.554

>»

0.85

1 >

0.684

>»

1.052

)»

120

0.786

120

1.208

> »

150

0.886

150

1.36

I. 10

0.433

104

^'ZS

0.655

J»

0.61

0.915

0.752

I-I3

> J

120

0.865

120

1.30

150

0.974

150

1.465

I-I5

0.474

1.40

0.705

0.665

»>

0.987

»>

0.821

»>

1. 216

»>

120

0.943

120

1.4

»»

150

1.064

>»

150

1.58

CARBURATION

Certain experimental errors have crept in, particularly
at the lower values, owing to the orifice at times becoming
partially fouled, but in the table these errors are neglected,
and approximately true values given by calculation, assum-
ing the square root law to hold good. On the whole, how-
ever, the experimental points have agreed very well, and the
curves have been plotted so as to average the results obtained.

In conducting these tests it was remarkable how easily

TO VACUUM PUMf *j|

JlIXt

to) "i

SCALE

TANK

JET
OVERFLOW-

-TO VERTICAL TUBE DIPPING INTO
VESSEL CONTAINING FUEL

Fig. 4. — Brewer's Apparatus for Testing Fuel Flow through Jet Orifices.

the flow through the smaller orifices became erratic, which
may account for the difficulty that is often experienced
in practice in running an engine very slowly for any
length of time.

The figures shown in the foregoing table were not
conclusive, so the author conducted numerous other ex-
periments with an instrument which he designed for
the purpose. This consisted of a long vertical tube,
into the base of which the desired jet could be screwed,

CHARACTERISTIC DISCHARGE

3-6

2-8

Eg 2-4

•^

s
-^

2*0

■^

1-6

I '2

0-8

o'4

■

,i/

' ,

x/i

7 <5

•^s/

f)-

\f\

'//

;>^

80 120 160 200 240

Velocity of Air in Fee/ per Second .
Fk;,. 5. — Observed Flow of Fuel through Circular Orifices.

280

CARBURATION

a manometer gauge being fitted, so that the depression
within the tube could be ascertained. Leading to the tube
was a fuel supply pipe, fitted with a small tank and con-
stant level device, the discharged fuel being led away by
a drain at the base of the tube. A vacuum pump was
attached to the top of the vacuum tube, so that any desired
vacuum could be produced in the tube, a manometer in-
dicating the vacuum or depression at the jet orifice.

Fig. 5 shows graphically the results of the experiments,
the air velocity in feet per second, corresponding to the
various suctions, being the abscissae, and the orclinates
being the gallons of fuel discharged per hour.

Studying these curves, we notice that at the lower
end, towards the origin, there is a lag in the flow due
to the surface tension of the liquid fuel. The fuel does
not emerge from the jet until the depression amounts
to 1 1 in. to I in. head of fuel. As the air velocity
increases by regular intervals, we find that the fuel dis-
charge values lie upon curves having a well-formed char-
acteristic. The shape of this characteristic depends upon
the shape of the fuel orifices and conditions of testing, and
one cannot say that a certain experimenter is wrong and
another right because the curves produced by different
methods of testing and with different apparatus do not
agree. The point is, however, that the fuel discharge
curves, obtained by plotting air velocity and discharge
in unit time, are not straight lines, but certain portions
of these curves are practically straight, and can thus be
utilised for working limits in any particular design of
instrument.

The Circular Jet. — The most usual type of jet orifice
met with in practice is circular. It is difficult to drill
accurately a true hole of small dimensions, and in ex-
perimental work errors in workmanship have caused much
trouble, as supposedly similar jets have varied widely in
their performance.

COEFFICIENT OF DISCHARGE 6l

A circular orifice is the fundamental feature of the Zenith
carburettor, and in designing the same, use is made of
Rummel's formula for rate of petrol discharge from a jet : —

where c\ and c.j are constants, being the coefficient of
discharge for the orifice.

The formula used in the experiments made by the
author to ascertain the value of c for petrol jets of the
dimensions ordinarily in use, was

where q is the discharge in cubic centimetres per second,
c is the coefficient of discharge,
w is the area of the orifice in square centimetres.
g is the acceleration due to gravity in centimetres per

second per sec. = 981
h is the head in centimetres over the orifice.

In the case of water it has been found that for pressure
heads up to 4 in. the value of the coefficient of dis-
charge varied from 0.738 to 0.770, the mean coefficient
being approximately 0.75, which agrees well with the value
0.77 given by Professor Unwin on p. 88 of his " Treatise
on Hydraulics."

This coefficient of discharge, however, applies only to
a -portion of the curve plotted with fuel discharge as
ordinates, and air velocity as abscissae.

Using Claudel jets, with the end screw removed so as
to eliminate the balancing effect of the tube, the author
found that at low heads the friction of the jet orifice is
very noticeable, and that as the diameter of the orifice
increases the coefficient of discharge appears to increase
also. He also found that, using water as the medium,
the surface tension of the water in a jet of i.io mm.
diameter is only overcome by a head of 10 to 15 mm.,
equal to an air velocity past the jet of 40 to 50 ft. per
second.

CARBURATION

If we examine the curves (Fig. 6) of discharge of
petroleum spirit from circular orifices, which are
drawn from the author's original charts, with the
difference that the abscissa are the square roots of the
water head in inches, the following characteristics will
be evident.

First, we note that the origin of the curves is, when]

Fuel Flow from Circular Orifices. Length of each Orifice, 5 times its
Diameter. Fuel at 55° F.

z
O
-I
_i
<

X y

X^^'^^.ililSl^^

Square Root of Head wj Inches of Water Pressure.
Fig. 6.

approximated by a straight line through each, located at
0.5 from the true origin. This corresponds with the
Brewer orifice, so we may, in fixing an equation for thesej
curves, base it upon {s/h — O.S) as in the Brewer orifice^
as the origin on the axis of -f. We then notice the method
in which the curve rises above the straight line drawn
through the false origin, to dip again in the centre and!

EQUATIONS FOR FLOW

rise at the maximum observed head. Supposing the
straight line of true flow be drawn through the true
origin, the deviation of the observed flow is still more
marked at the upper ends of the curves.

The small orifice tested by Rummel does not show
so great a deviation, no doubt due to its small dimensions.
The author found that the error increases with the size
of the orifice, probably showing that the proportionate jet
friction is greater with the smaller orifices even at higher
rates of flow.

Only an approximation can be made to an equation
for these curves, in terms of y = m(ji:—c), where m is the
tangent of the angle, and it will be seen that approximately
the flow of fuel in terms of the area of the orifice and the
square root of the head is as follows : —

O = flow in gallons per hour.

/i = head in inches of water pressure.

Table XXIV. — Equations for Flow Curves, Circular

Orifices.

Diameter of
Orifice, mm.

Area, sq. mm.
= A.

Values of Q — the Flow in Gallons per
Hour of Petrol in Terms of (V/i - 0.5) x »i.

1.40

1-54

( JA-o.s)

A
1.54

1.20

1-13

0.8 (v/A-o.5)

A
1.4

1.05

0.86

0.66 ( J/t- 0.^)

0.90

0-635

0.45 (J/i-o.s)

A
1.4

0.85

0.54

0.33 {J^i-0.5)

A
T.63

CARBURATION

The last column gives the flow of fuel approximately
in gallons per hour per square millimetre of orifice area,
taking into consideration the pressure acting in accordance
with Unwin's formula on p. 6.

For example, Q = o.33( \/// — 0.5) for an orifice 0.85
mm. diameter, but this is only approximate throughout the
whole working range.

To bring these orifices into line with others under con-
sideration we will endeavour to find the constant K, relating
one sized orifice to another, and for this purpose the
following table is taken from the foregoing curves for
orifices of various sizes giving the same flow of fuel under
different heads : —

Table XXV. — Flow, i Gall, per Hour, Circular
Orifice, with Spirit.

sih.

Area.

;/Ax(V//-o.5).

Inches.

Sq. Mm.

3-7

0-54

0-57

1-75

2.7

0.635

0.63

1.59

2.3

0.86

1.02

0.98

1.8

1.13

1. 17

0.855

1-3

1-54

1.23

0.815

That is to say, that K«a( \//^ — 0.5)= i gall, per
hour, i.e., 1.75 xo.57— i, and from the above it will be seen
how much the value of K varies with the area of the orifice.

In the above table n is a factor relating the areas and
the square root of the head for their different values.

These figures should be compared with those given for
the Brewer orifice on p. 96.

Take for example a flow of petroleum spirit of 2 galls,
per hour through a circular orifice.

RELATIONS BETWEEN AREA AND PRESSURE 65

Table XXVI. — Flow, 2 Galls, per Hour.

Diameter of

Area,

Head in inches

ijh

Jet, mm.

sq. mm.

of Water.

inches.

(AV;4-o.5).

1.40

1.54

6.3

2.46

3.02

0.663

1.30

1-33

7.0

2.55

2.73

0.732

1.20

1.07

9.5

3-09

2.77

0.722

1-15

1.02

10. 0

3.16

2.72

0.735

1-05

0.86

13.0

3.61

2.68

0.746

1. 00

0.785

14.3

3.78

2.58

0-775

0.90

0-635

16.7

4.10

2.29

0.875

For

water these /i

igures become

1.20

1.07

12.0

3-47

3.18

0.63

115

1.02

i8-S

4.31

3-89

0.514

r.oo

0-95

19-5

4.42

3-73

0.535

In the above calculation an attempt has been made to
show the relation existing between the flow of fuel through
the orifice, the area of the orifice, and the square root of the
pressure head, and a multiple K is introduced representing
a factor relating the variables, as follows : —

We find that a flow of 2 galls, per hour is produced
by any of the combinations in the above table, and if the
discharge curves were straight lines having an origin along
the line of abscissae at a distance equal to Jli — o.^, the
value a(\/^— 0.5) multiplied by the tangent of the angle
between the curve and the base line, would indicate the
curve of fuel discharge. A figure represented by K is
here introduced, and referring to the curve (Fig. 6) and
the table above, we will take, for example, the orifice 1.13
sq. mm. area and locate the curve of fuel discharge.

When \/^ = 4.0, J = 2.9, and 4.0-0.5 = 3.5, therefore the
tangent of the angle of the curve whose origin is on the

2 Q

axis of ;ir at position 0.5 =—^ = 0.83, and the flow in gallons

per hour at any suction = the square root of the suction in
5

CARBURATION

inches of water head minus 0.5 in inches of water head x 0.83,
approximately, as the curve is not a straight line.

This value does not take into account the area of the
orifice, and for this reason the value of K is adopted, which
includes the tangent of the angle and the area of the orifice.

It will be interesting to note how the foregoing figures
compare with the results of Professor Morgan's experi-
ments, which were carried out on somewhat similar lines,
though the areas and characters of the orifices were not
made known.

The author has endeavoured to calculate as nearly as
possible the air velocities and depressions from such data
as are available, and has taken the velocity of air through
the choke tubes from the known volume of air passing,
divided by the area of the choke tube. This is not, of
course, accurate, as no account is taken for the coefficient
of the choke tube ; but in the absence of data as to its
shape, it has been thought better to ignore this factor.
When examining the tables, therefore, only relative and
not actual values must be considered.

The figures have been worked out and arranged so as
to be comparable with others in this book. The coefficient
of discharge of the orifice should be particularly noticed.

Table XXVII.— Computed from Fig. 8 in Prof. Morgan's Paper.
Choke, I in. diameter. Area = 0.44 sq. in.

Cub. ft.

Velocity
of Air
Plow,

Equivalent
k in inches

V^.

per min.

Vft.

of Water.

Cub. cm.

Galls, pel

per sec.

per min.

hr.

19.5

107

2.8

1.67

0.66

148

6.0

2.45

0.99

187

8.5

2.92

100

1.32

224

Ti-5

3-4

125

1.65

268

14.5

3-8

150

1.98

306

17.5

4.2

175

2.31

v/^-0.4

-c.

0.52

0.48
0-525

0-55
0.582

0.608

Air curve, false zero, at 27 ft. per sec. velocity = o. 1 7 in. of water.

PROFESSOR morgan's EXPERIMENTS

Table XXVII. {continued).
Choke tube, i in. diameter = 0.785 sq. in. area.

Cub. ft.

Vft.

per min.

per sec.

1 10

^SZ

183

Equivalent
h in inches
of Water

I.I
2.8
6.1

8.5

.//;.

1.05
1.67
2.48
2.92

Cub. cm.
per min.

75
100

Galls, per
hr.

0.66
0.99
1.32

V/^-o.4

= C.

0.508
0.520

0.475
0-525

Air curve, false zero, at 24 ft. per sec. velocity = o. 1 6 in. of water.

We will now examine in the same manner Professor
Morgan's curve, as shown in Fig. 13 of his paper before
the Institution of Automobile Engineers {Proc, vol. v.
p. 50), in which the flow of fuel is plotted with the
square root of the head. In this example the effective
heads are much smaller than are usually met with in
practice. The author has prepared the following figures
as accurately as possible from the printed graph. The
author, however, thinks that the line connecting the
observed points is incorrectly drawn, as it should not go
directly to the origin, but the figures are taken from the
curve showing no false zero.

Table XXVIII.-CoMPUTED from Prof. Morgan's Experiments.

sih

Q=c.

Mm. of
Water.

Inches of
Water.

Cub. cm. per
min.

Galls, per
hour.

6
8

17-5

22.5

27
32
37

0.23

0-315
0.512

0.69

0.89

1.06

1.26

1.40

25
50

TOO

125
150

175
200

0-33
0.66

0.99

1.32

1.65

1.98

2.31

2.64

1-43
2.09

1.93
1.91

1.85
1.87

1.83
1.88

68 CARBURATION

If one studies the action of carburettors of the Vapour
or Zenith type, the shape of the characteristic curve of
petrol discharge through a small orifice must be borne in
mind, and the position of the normal working of the main
jet must be located upon this curve. In the ordinary
single-jet carburettor it is the custom to allow such relative
dimensions of jet, air passage, and other ruling factors that
the single jet is of sufficient size to pass the necessary
quantity of petrol at low speeds. At high speeds, there-
fore, either air must be added or the normal suction
decreased, so that, as the upper portion of the discharge
curve is worked upon, there is no excess of fuel discharge.
In the Zenith and Vapour carburettors the size of the
normal jet is arranged so that its working range is on the
upper portion of the discharge curve, which is practically
a straight line. Such a jet is too small to give a sufficient
discharge at low suction values, and a supplementary
supply of fuel must be admitted in order to produce an
explosive mixture. This supply is regulated by a separate
jet, giving a more or less constant discharge, and in the
Vapour carburettor the size of the small air admission hole
above the petrol well regulates the amount of fuel which
can flow through the by-pass hole, and, incidentally, has a
marked effect upon the compensating flow at low speeds.

Varying speeds at varying loads are demanded with
different fuels under different conditions of atmosphere
and temperature, and these conditions cannot all be
met successfully by any ordinary single-jet carburettor, by
reason of the principle upon which it works. The addition
of spring-controlled extra air devices to meet such con-
ditions cannot produce satisfactory or correct results for
modern demands. An attempt is sometimes made by
such means so to adjust the tension of the spring and
the shape and size of the orifices that the additional air
admitted shall correct errors which creep in at high engine
speeds. For all practical purposes, however, devices of
this nature do not work well for any length of time.

THE OBJECT OF TWO JETS

The majority of multi-jet instruments have been pro-
vided with several jets of different dimensions, working in
choke tubes of various sizes, so that for various engine
demands either one or the other or a combination of jets
comes into action.

Let us now for a moment consider the straight part of
the curve for a circular orifice, such as will exist between
the limits of about 5 in. and 20 in. of head for the type
of orifice under discussion. These limits are quite usual
in ordinary practice, but, of course, the modern engine
runs the depression much higher than the upper limit
here mentioned in many conditions of working.

We will take an experiment with water, which, as we
know, is more viscous than petroleum spirit by 10 to 20
per cent, according to its temperature, as will be seen from
Sorel's table, p. 53, and the author's experiments, which
show approximately 15 per cent, increase of viscosity of
water as compared with benzene.

Table XXIX. — Circular Orifice (Discharge of Water).

Head.

Discharge.

Increment of Discharge.

By Experiment.

Air Theoretically
through a Tube.

Inches.

5
10

15
20

Pints per hour.

9
13
17

1.50
2.17

2.84

I.41

1.73
2.00

In the above the increase from 6 pints to 9 pints is
1.5 times the quantity, whilst, according to the law for air
flow, the amount of air passing through a Venturi tube
will vary as the square root of the increase of pressure
difference. The pressure difference in this case is 2, i.e.^
10 in. is twice 5 in., and the square root of 2= 1.41.

CARBURATION

If reference be now made to the author's characteristic
curves for petrol flow, and the same sized orifice be taken,
viz., i.io mm. diameter, and conversion be made into pints
of fuel per hour instead of gallons, the following relations

hold good :-

Table XXX. — Circular Orifice with Petrol at 55° F.

Head in

Inches over

Orifice.

Pints of Fuel
Discharged
per Hour.

Increaseof Dis-
charge per cent.
Compared with
Water.

Increment of Discharge.

Fuel.

Theoretical

Air through

a Tube.

5
10

I.S

8.65
14.0
20.0
24.0

14.4

15.6

15-4
14.2

1.62
2.31

2.77

I.4I

1-73
2.00

The differences in the third column are evidently due to
slight experimental errors.

The discharge of fuel from the orifice is not directly
proportional to the square root of the head, nor yet to any
definite relation, as, for instance, it may

= c X

0.S/1+ sih

where c

2.50,

= c X

o.2 5i^+ slh

where € = 5.

The former holds good for lO-in. and 15-in. heads, whilst
the latter applies to 5-in. and 20-in. heads, for a jet orifice
of I.IO mm. diameter and 5 mm. long.

In order to bring the fuel discharge through various
shapes of orifices into line the author calculates the dis-
charge in gallons per hour per square millimetre of orifice,

and this value is designated by the symbol -, and from this

can be found the coefficient of discharge of the orifice, as
for example : —

■^ O

p o .

aM0:39 iJ3d i23J M

HI if iO MI3013A

CARBURATION

To find the coefficient of discharge c —
q = coi sl2gh as before.

Where Q = the discharge in cubic centimetres per second = q
(gallons per hour) x 1.26.

0) = area of the orifice in square centimetres =

= head in centimetres.
^=981 cm. per second per second.

For lo-in. head = 25 cm. —

q _ Q X 1.26 _Q

100

c =

\l2gh
for 15-in. head = 38 cm.

A / A

\/2 X q8i X 2<

100 ^ ^

X 0.568;

^ = ^x 0.463;

for 20-in. head = 50.8 cm. —

for 25-in. head = 63.5 cm.

c=- X 0.400 ;

<^ = -x 0.356.

We will take now the flow of water through orifices a
in the following table and find the coefficients of discharge.

Table XXXI. — Circular Orifices.

Water Flow in Gallons per Hour and Coefficient of
Discharge of the Orifice.

Jet.

lo-in

Head.

i5-in.

Head.

20-in

Head.

Diameter,

Area,
Sq. mm.

Flow in
Gallons

Coefficient
of

Flow in
Gallons

Coefficient
of

Flow in
Gallons

Coefficient
of

mm.

per Hour.

Discharge.

per Hour.

Discharge.

per Hour.

Discharge.
0.906

1. 10

0.94

1. 12

0.680

1.63

0.800

2.13

I-I5

1.04

1.56

0.855

1.78

0.795

2.19

0.842

1.20

I-I3

1.85

0.930

2.25

0.925

2.62

0.930

1.30

1.32

2.38

*1.02

2.93

*1.03

3.50

*i.o6

* Where the coefficient is above unity the result niay be attributed to some
slight experimental error.

CHAPTER VI

THE ANNULUS

The Annulus. — The modern development of carbu-
rettor practice along the lines of constant depression
has led to the adoption of the annular orifice to a great
extent.

When one comes to consider a varying orifice of this
type scientifically, one has to deal with a problem of some
importance and difficulty, for we find that with a pin of
straight taper the increase in the area of the orifice is not
proportional to the movement of the pin. Furthermore,
we find that as the pin is gradually withdrawn from the
orifice, the ratio of the length of the orifice to its effective
area varies from moment to moment. For this reason a
correctly designed modulating pin requires very careful
thought and a large amount of experimental work. Even
then grave errors are likely to creep in, due to the pin not
lying centrally in the orifice. One cannot generalise a
modulating pin design. We will, therefore, consider pins
of i6 to 25 mm. long, fitting into orifices of 3.9 mm. to
3.96 mm. diameter, as with this type of pin the author has
had considerable experience.

We will take as the first set of examples a pin 16 mm.
long, 3.9 mm. diameter at the thickest end, and 3.45
mm. diameter at the tip, working in an orifice 3.8 mm.
diameter. When water was passed through the orifice
under a head of 10 in., the following rates of flow of
fuel per hour and times for a discharge of half a pint were
noted.

74 "^^^^B CARBURATION

Table XXXII.
Pin 1 6 mm. long and 3.9 to 3.45 mm. diameter.

Position of

Time for

Pin from

\ pint-

Zero in mm.

seconds.

630

400

290

235

195

165

Flow of
Water in

gallons
per Hour,

0.36
0.56

0.75
0.98

1. 18
1.38

Area of

Gallons

Annulus,

per Hour

sq. mm.

persq.mm.

0.865

0.415

I-I75

0.64

1.49

0.79

Coefficient

of Discharge

of the

Orifice.

244

376
464

This flow, it will be seen, is remarkably small, and is due
to the high jet friction ; also it will be noted that the co-
efficient of discharge of the orifice increases as the time
of discharge decreases.

Let us now consider a modulating pin 18 mm. long,
4.05 mm. diameter at the root, and working in an orifice
3.96 mm. diameter, and again the same pin working in an
orifice 3.80 mm. diameter. The pin in this case was marked
off in intervals of 2 mm., and at each position experi-
ments were made on the rate of flow of fuel in gallons per
hour, and calculations deduced therefrom. Water was
used as the liquid, with a pressure head of 10 in. over the
orifice. Table XXXIII. shows the results obtained.

An attempt was made in designing the above pin to
produce a flow of fuel as nearly as possible in proportion MX
to the flow of air, and it was so set in the orifice that in
normal zero its position was 2.5 mm. from the root, i.e., the
area of the annulus in the slow running position was
0.6 sq. mm. HI

This pin was designed by the author for a suitable
carburettor for a 3-litre engine, and its effect is shown in
the following curve.

RELATIONS BETWEEN AREA AND DISCHARGE 75

Table XXXIII. — Special Pin i8 mm. Long, with Increased
Taper, Starting io mm. from the Root. Diameter, 4.05
mm. at root, and 3.06 at tip.

Diameter of Jet ^ 3.96 mm.

Position of Pin

Area of

Flow in

Gallons per

Coefficient

in mm. from

Annulus,

Gallons per

Hour per

of Discharge of

the Root.

sq. mm.

Hour.

sq. mm. of Area

the Orifice.

0.5

zero

2.0

0.5

1.22

2.44

1.39*

4.0

0.90

I.4I

^•57

0.89

6.0

1.40

1.80

1.28

0.725

8.0

1.80

2.02

1. 21

0-635

Diah

leter of Jet, 3.

80 mm.

8.0

0.8

0-55

0.69

0.390

10. 0

I.I

1. 21

I.I

0.625

12.0

1.9

2.0

1.05

0.595

14.0

2.6

2.8

1.07

0.610

16.0

3-3

3.46

J-oS

0.595

18.0

4.0

4.1

1.03

0.585

This curve and diagram show first of all a sweeping
line from the left-hand top corner to the lower right corner,
representing the time taken for a measured quantity of
fuel to flow through the orifice in different positions of the
pin, and it will be at once apparent that the initial incre-
ments of orifice opening show rapid increases in the fuel-
flow. However, when the pin has lifted about 5.5 mm.
the curve tails off, or in other words, the fuel-flow does not
increase rapidly enough, and the characteristic of fuel-flow
for this type of orifice shows a decided droop as the size
of the orifice increases. In order to overcome this ten-

* This value appears to be exceptional, and must be considered with
caution.

76 ^^^ CARBURATION

dency the modulating pin must be modified in shape7

A ir in litres per minute. Flow in gallons per hour.
% % t ^ ^ \

Flow in aallons fxr hour

/
/

%
&

\
\

L N

:t-.

. ^

3*.

P^iG. 8. — Curve of Fuel discharge through Annulus 3-litre Engine.

and the time curve was taken before the pin was
modified.

AIR AND FUEL FLOW

Passing now to the desiderata of the pin, an air curve is
plotted to some convenient scale of ordinates so that the air
passing will correspond correctly with the fuel required.

100

6 % A 6 S 10 IZ ti-

Fig. 9. — Flow of Air through i^-inch Venturi Meter.

Take, for example, a 3-litre engine : we find that for 100 per
cent, volumetric efficiency at a speed of rotation of 1,000
revolutions per minute 1,500 litres of air and vapour pass
through the engine.

CARBURATION

For convenience and ease of calculation we will neglect
the volume of the vapour and take as a round figure
10,000 volumes of air to i volume of liquid fuel. Then we
find that the fuel required per minute is : —

I coo X 1000

-^ = 150 c.c.

10,000

per minute,

150X60 o 11 1

-^ = 1.98 galls, per hour.

4540

It will be seen from experiment that this flow is given
with a pin lift of 6.5 mm., but for convenience of the air
scale, and in order to separate the air and fuel curves, a
scale has been taken for the air curve which slightly fore-
shortens it and increases the inclination of the air curve.
It is obvious, however, that the mixture will be slightly
on the weak side at high speeds unless, of course, the suction
is increased by fitting a suitable stop to prevent the air
valve rising above a certain maximum. The author has,
therefore, found it advisable in some instances to fit such
a stop so as to limit the lift of the air valve to 8 or 10 mm.
as the case may be, so that a sufficient flow of fuel will be
provided when high engine speeds are required. Another
method of attaining this end is to choke the air inlet
aperture so that the depression within the instrument will
be increased under high speeds of working of the engine.

We will consider for a moment a few figures taken
from a careful test with such a carburettor, not in any way
specially prepared but a stock instrument.

Table XXXIV.— Full Load.

Revs, per
. Min.

Diameter
of Pin.

Area of
Annulus.

B.H.P.

Fuel
Con-
sumption

Pints per
B.H.P.
Hour.

Lift of
Valve

Coefficient
of Dis-
charge.

Pints per

mm.

Sq. mm.

Hour.

mm.

500

3.80

0.94

8.25

10.5

1.27

2-3

1.40

0.795

1,000

3.61

2.08

19-5

16.95

0.87

5-0

1.02

0.568

1,800

340

3.22 26.1

21.9

0.84

8.0

0.85

0.483

CONSUMPTION TESTS

The size of the engine is not given, but it is a standard
type by one of the best known English firms with reason-
able valve dimensions.

The fuel consumption was high, as the engine was a
new one and rather stiff.

Table XXXV.— Half Load.

Revs, per
Min.

Diameter
of Pin.

Area of
Annulus.

B.H.P.

Fuel
Con-
sumption

Pints per
B.H.P.
Hour.

Lift of
Valve.

Coefficient
of Dis-
charge.

mm.

Sq. mm.

Pints per
Hour.

mm.

500

3.86

0-55

4-13

6.95

1.68

1. 5

1.58

0.90

1,000

3-75

1.25

9.75

12.0

1.23

1.20

0.68

1,800

3.61

2.08

13-05

i5-f

1.20

0.94

0.534

The examples given for the flow of fuel in the above
table are typical of many figures obtained, and may
perhaps be amplified by the following, taken from the
same series of tests with a slightly different shape of pin.

Table XXXVI.

Area of

Coefficient

Area of

Coefficient

Annulus,

sq. mm.

Discharge.

sq. mm.

Discharge.

0.94

1.58

0.895

3.10

0.882

0.500

1.72

1. 00

0.568

3.22

0.85

0.483

2.08

1.02

0.580

4.64

0.645

0.36

2.44

1.03

0.587

5.20

0.607

0.34

2.54

T.02

0.580

It may be interesting to the reader to study an example
of the results obtained by the author in America with a
carburettor given to him to develop at the laboratory of
the Automobile Club, New York.

As received the instrument was very erratic, and would

CARBURATION

not work, although a great deal of time had been

spent^.

upon it by American engineers.

The author started by calculating, on a purely theoretical
basis, the sizes of the air orifices and the dimensions of the
tapered modulating pin, and personally constructed those
parts in the laboratory, the whole work occupying one day.
On the following day, the carburettor was attached to the
engine, and without any trial and error adjustment the
following authoritative results were obtained : —

Table XXXVII.
Tests on Carburettor in New York.

Dynamometer

Weight

Engine Revs.

Force in lbs. at

B.H.P.

of Fuel per

per Minute.

the End of the

Hour.

B.H.P. Hour.

Arm.

lb.

405

37.1

8-57

8.8

1.03

1,012

39-1

22.6

15-2

0.672

1,300

35-9

26.7

16.9

0.632

1,620

30-7

28.4

180

0-635

1,830

27-5

28.7

19.6

0.683

From the above table the fuel consumption results
will be seen to be entirely satisfactory for American
gasolene, especially when compared with the majority of
results obtained with American carburettors in the
same laboratory, none of which had shown such a low
consumption.

Before leaving the subject of the taper pin we will take
a limiting case, assuming the hole has a diameter D = 8 mm.

The pin has a diameter ^1 = 7 at 2.5 mm.

^2 = 6 „ 5 mm.

^3=5 M 7-5 mm.
^4 = 4 ,, 10 mm.
^5 = 3 » 12.5 mm.

►from the root.

AMERiCAN TESTS 8 1

The respective areas of the annular orifices will be in
proportion to the difference of the squares of the diameter
of the pin at any position, and that of the orifice multiplied

by -, which we will write K. . For any other sizes of orifices

4
the fuel area will be some function f of the areas here
calculated.

J^_ I then A- (64-49)k=i5K\
^^1-7^ \ I3K

then a = 28k -

IIK

D = 81 ,, /

, \ then A= •^QK - - \ ^

4-5/ \ 5K

J \ then a = 48k - - -/ ,

^^ = 4) \ ^^

^ = ^1 then A = 55K - - - /

If the air valve opening is proportional to its lift it will
be seen that by the above reckoning the increment of fuel-
flow is a great deal slower than the increment of air-flow
under the same conditions in all cases. However, when
the air valve opening is small, the coefficient of flow of
the air orifice must be taken into account, as a greater
valve area will be required to pass through the quantity
of air, and this increase of air opening will also give an
increase of fuel opening.

If, however, we write A as the air opening at a lo mm.
valve lift, and c as the coefficient of discharge of the air
orifice, we have the following table for comparison and
upon which to base the design of the air orifice.

In practice, when the valve is large, it will be found
that its lift is practically proportional to the demand of
the engine, so we may write : —

CARBUkAtlON
Table XXXVIII

Coefficient of

Lift.

Fuel Area.

Air Area.

Discharge of the
Fuel Orifice.

Fuel Discharge.

mm.

2.5

/15

0.25 A

0.900

/J3-5

5-0

/28

0.5 A

0.725

/20.4

7.5

/39

0.75 A

C.635

/24.8

10. 0

/48

1. 00 A

0.600

/28.8

12.5

/55

1.25 A

0-550

/30-2

The area of annulus is proportional to the square of the
lift of a V-shaped measuring device.

CHAPTER VII

BREWER'S FUEL ORIFICE

Having now considered the fuel discharge from a circular
orifice, and from an annulus, it is evident that in both
systems there are certain defects which are difficult to
overcome in practice. For this reason, the author care-
fully studied how it would be possible to design an
orifice that would give a rate of fuel discharge closely
approximating the flow of air through an aperture of
ordinary formation, that is to say, that the flow of fuel
should, as nearly as possible, approximate to the square
root law or the discharge curve should be similar to that
which is shown for the flow of air on p. 71.

The author considered that it was possible to design
an orifice which would combine the characteristics of the
circular hole and the annulus, i.e.^ instead of the flow of
fuel tending to increase (as shown by the curve having an
upward trend) in the case of the round hole, and tend-
ing to lag (as shown by the curve's downward trend) in the
case of the annulus, a composite orifice could be formed,
so that the rate of flow of fuel would be a mean between
the two. At the same time the orifice would produce a
high friction, and give a low and practically constant
coefficient of discharge under all ordinary working
conditions. With this object in view, the first point to be
considered was whether the orifice should be vertical or
inclined, and furthermore whether a modulating pin of any
particular shape and position would be necessary. The
author decided that a modulating pin which was hanging
in a vertical position would be the most suitable, and that
this pin should not be liable to cause any error through

84 ^^^^^^ CARBURATION

displacement in the orifice. For this reason he decided
that the modulating pin should at certain points touch
the orifice, or nearly do so, and should always be located
within the orifice, so that it would not be liable to dis-
placement under any set of conditions. Furthermore, it
was considered necessary that any adjustment of the
modulating pin should, if desired, be made whilst the
engine was running, and that this adjustment should in
no way entail any risk of leakage of air or fuel.

In many systems of modulating pins in carburettors it
is only possible to make adjustments to the pins by dis-
mantling the carburettor, or by screwing some device or
holder into a gland which is more or less petrol tight.
Such an arrangement is bound to be inconvenient, par-
ticularly as, when it is in an inaccessible position, it is
impossible to see the amount of adjustment which has
been given, or the amount of movement imparted to the
pin as the carburettor works. In such a delicate arrange-
ment as a carburettor adjustment, it is a sme qua non,
first, that the adjustment should be visible, and second
that it should be accessible. It should also be possible
to locate the adjustment at any time so that in the event
of the carburettor being taken down, or being deranged
by an inquisitive chauffeur, it is an easy matter to fix the
adjustments in their original or predetermined condition
without loss of time and with a maximum of accuracy.
Having all these points in view, the author decided, first,
that no system in which the modulating pin passed through
the fuel path would be feasible, and second, that the only
system possible would be one with the pin hung in a
vertical position and readily accessible without in any
way interfering with any of the arrangements of the
carburettor itself With these objects in view the
author has designed a modulating pin which is shown
on pp. 88 and 163, and which has the .following
characteristics. First, the coefficient of discharge of the
orifice is practically constant under all working con-

CHARACTERISTIC FEATURES OF BREWER ORIFICE 85

ditions, i.e., whether within the Hmits of working the
head is small or great. Second, in any position of the
pin, whether the orifice is large or small, the coefficient
of discharge is not affected to any noticeable extent.
Third, the jet friction is high, and thus the effect of
inertia is counteracted to a very considerable degree.
Fourth, when the pin is in a neutral position, or when
the throttle is suddenly closed, the pin automatically
falls back in the orifice and prevents any excessive flow
of fuel which might otherwise ensue (due to the inertia
of the fuel itself in the fuel passage). Fifth, the zero
position of the pin can be absolutely and easily deter-
mined, as whatever adjustment of the carburettor is made
for various proportions of mixture, the zero position can
be always returned to, and is unaffected. Sixth, the pin
can be taken out of the carburettor without any loss of
fuel, and it can be dismounted with a minimum of effort
in a i^yf^ seconds. If it is desired to make any alteration
to the pin, or to change it, this can be done by hand
without the use of tools, and a new pin can be substituted
in a few seconds. Seventh, the pin is a good size, and
in using a large pin it is much easier to work upon it and
tq make any adjustments than would be the case where
a very small pin is employed. Eighth, the surface of
such a pin is large, and therefore the wear, if any, is
distributed over a large area of contact, though in this
case the surfaces are not actually in contact, but are
separated by a film of liquid.

If we look into the theory of this particular type of
orifice, we must embody with the shape of the pin its
surroundings and working conditions, and combined with
this pin is a jet tube of ample dimensions, having an
exterior formation as shown upon the drawing. This
exterioj formation, in combination with a small Venturi
tube, forms a very important feature of the Brewer car-
burettor, which is the atomising of the fuel as it issues
from the jet. The atomising is carried out by concentrat-

86 ^^^^ CARBURATION

ing the air flow in the vicinity of the fuel orifice at all
times, and so arranging the Venturi tube that within certain
limits of working this concentration is carried out, as the
minimum area between the Venturi tube and the exterior
of the jet tube is located round the largest part of the jet
tube, until such a time as the Venturi tube lifts above the
jet tube to a distance which makes the annulus between
the Venturi tube and the modulating pin smaller than that
between the Venturi tube and the exterior of the jet tube.
This is somewhat difficult to explain, but it can easily
be shown mathematically, and it is important that until
a predetermined limit of working is reached, a high velocity
of air be concentrated round the jet. When a tendency
occurs for the jet to over-discharge under a high velocity
head the area around the jet is increased. Only sufficient
air is allowed to pass through the Venturi tube and round
the jet tube in ordinary working, to produce slow running
of the engine and car speeds on the level up to about
lo miles per hour. It is at such a speed that in a two-jet
carburettor the smaller jet is in operation. To obviate the
necessity of a number of jets this internal Venturi tube
arrangement is resorted to. By means of it a very fine
spraying of the fuel is possible, and the issuing stream of
fuel passes up the centre of the air valve and is deflected
by the deflector plate on the modulating pin carrier and
throughout the mixing chamber of the carburettor. When,
however, the engine demand increases, that is when the
depression within the mixing chamber has reached about
lo in. of water head, and the fuel curve of an ordinary
single-hole jet orifice begins to flatten out, the carburettor
works in the usual way, proportioning the fuel orifice to
the air orifice, and so on throughout the range of working
until the upper limit is reached. When, however, this
point is arrived at, a certain important law is brought into
requisition, and if one study the question of vapour pressure
in Chapter II. one will see that as a mixture becomes richer
its vapour pressure increases. It is therefore intended in

EFFECT OF VAPOUR PRESSURE UPON DISCHARGE 8/

this arrangement, where fuel is vaporised in the centre of
an air valve, to take advantage of the increase of vapour
pressure at such times as the vapour pressure tends to
increase, due to the tendency to enrichment of the mixture.
For instance, supposing there is a depression equal to

§
1

a: -*

^/'^

f ^'l

2 «

T 9

12 S

.<'

K-^'

;-'

^ ■

r-'"

raf**^

.^--

10 IS 20 2S 30 36 40 45 50 55 60

Temperature in Degrees Centigrade.

6iS 70

Fig. io.— Curve of Vapour Pressure for Saturated Vapours.

25 in. of water head in the mixing chamber of the
carburettor, it does not follow that this pressure is actually
operative at the jet orifice, as the pressure at this point
is due to the difference between the negative pressure in

CARBURATION

the mixing chamber and the positive pressure which is due
to the vapour pressure of the fuel. Of course vapour pres-
sure only can occur where vapour occurs, and in designing
this carburettor the amount of air which is allowed to pass
primarily around the jet is small, about lO to i8 per cent.
of the total when the air valve is in operation, thus causing
the vapour which comes up the centre of the
air valve to be more or less saturated. The
extent of the saturation will usually depend
upon the temperature of the air which is
admitted around the small Venturi tube.
With this object in view the carburettor has
been so designed that a specially hot-air
supply can be introduced to this portion of,
the instrument, and hot air can be taken from
any desired position.

It is not intended in this chapter to dis-
cuss the question of the carburettor or itsq|
merits, but simply the effect of the orifice,
and this is all bound up in the question of
vapour pressure as well as in that of the co-
efficient of discharge. Now with reference to
this coefficient, we will for a moment study
a few figures to show how the size of the fuel
apertures are arrived at, and it may be men-
tioned that an important feature of this type
of orifice is the exact shape of the flutes
which are formed in the sides of the modu-
lating pin. These flutes, instead of being of
an ordinary V shape or slits, are formed of a
semicircular section with rounded corners
where the flutes run out into the circum-
ference of the modulating pin. At the upper
end of the fluted part a slight taper is given
to the pin so as to deflect the fuel stream,
and at the same time to give a positive .

Fig. II.

position for slow running.

AIR AND FUEL FLOW

f ■■

i^T/'

^x^

mJ"

28
3 5*

, 'SL

.^'

,<^

.fCc*

^-«

<l(

/rrltj^

fUZZ

/*^

5;^

^^^

"^^

eTi*^*^

ai*J

^ ^

^t^j

yjlf^

jtT

Th«<

rf^i

iZJZ

rfi

)U'__

— -

- "^

__--

^■'■

— ■

Head in inches of Water /iressitre.

Fig. 12. — Flow of Water through Brewer Orifices.

CARKURATION

<
u

fa
o

H
<

o
Pi

;^
o

►J

X
X

. c <« «

^"^ij-a

•

•a

'S O y

tt, en

h-t

U-5

'3 i-

t5-

0«

C en ttJ

0) O (J

cl
4/

u->

o •

t-^

ES"

n§

:SS

r—

■s ^^

Tj-

^s,

c Jj *>

>-t

S,E

ffi

l>-

r«.

!>.

ji *-

og.

C J) «

■ 4)-- be
O-r; Q iH

*> o o

P.E

ffi

o .

t--.

to
d

t-l

U-)

O «

_
c .

rcr

fa <n

'•si

Tj-

•-

J .s

TESTS UPON DISCHARGE FROM BREWER ORIFICE 9 1

Table XL. — Calculation of Area of Orifice (Brewer's

Patent System).

Revs, per
Min. of
Engine.

Air Velocity, 200 Ft. per Sec.

Lift of
Modulat-
ing Pin.

Area
through
Flutes.

Flow of
Fuel.

Fuel Circular
Required. Orifice.

Annular
Orifice.

500
1,000
1,500
2,000

Gals, per
Hour.

0.99
1.98
2.97
3-96

Area

Required.

Sq. mm.

0.81

1-43
1.65

Area
Required.
Sq. mm.

0.90

2.0

3-3

4.0

mm.

as set

8.0

16.0

Sq. mm.
1.62

3-2

4.5
6.0

Gals, per
Hour.

0.99
1.96
2.97
3-96

We see from the above table that the combined area
of six flutes at a distance of 16 mm. from zero is 6 sq. mm.,

Flow of Water from Brewer Orifice

2 3 4 5

Square Root of Head in Inches of Water Pressure.
Fig. 13.

CARBURATION

2.^., the area of each flute is i sq. mm. A sectional
contour, plotting areas of orifice with linear movement,
does not give a directly proportionate increase of area,
as special provision has been made for ease of starting
with cold fuel and air.

The following table is compiled from a series of curves,
the result of experimental work both on positive pressure
discharges through this type of orifice and from measured
fuel consumptions of an engine on the test bench. In
order to ascertain the area of the orifice, the pin position
during the various tests was noted, and from an enlarged
diagram of the flutes these areas have been calculated.
The figures given are mean values, and experimental errors
have been as far as possible allowed for.

The suction was measured directly by a water mano-
meter, but in the pressure tests the fuel head was taken,
due allowance being made for the specific gravity of the
fuel.

USEFUL DATA

a;
w

m
Z

►J
<

H
o ^^

< d

g ^
> O
H .

"^ a,

2
O

•J

«4-l

{/5

^ u:

y (u

\<i

;

-'.

)_4 a

•

«>

T3-'

h-"

U-)

t--

•

t-^

•

1-4

Tl-

fT)

vr>

t-^

Tl-

>-t

•

(-4

•

i-i

1— 1

rr>

1-4

)— (

*~'

t-H

U-)

■<*■

1-H

;

Tt-

1-^

■"■

t-H

h-<

h-l

•

!>.

1— 1

H-l

^-l.

>-l

t-i

•

1— 1

CARBURATION

The equation to the curve for an orifice 2.4 sq. mm. in
area is : —

y = m{x - c) where ^ = 0.4,

4.6

jk = 0.55(^-0.4).

Area.

Tan. of Angle.

Flow, Galls, per
Hour.

Sq. mm.

5.6
4.8
4.0
3-2

2.4

1.6
1.2
0.8

1.48

0.965
0.785

0-55

0-39
0.234

0.195

1.48 (J/l-0.4)
1. 15 {s/7z_-0.4)
0.965 ( J/l- 0.4)
0.785 ( s/X- 0.4)
0.55 (n//^-o.4)
0.39 (n//^-o.4)
0.294 ( Jk- 0.4)
0.195 ( v'^- 0-4)

To find the flow of fuel from a Brewer orifice when the
area of the flutes is known, it has been found from experi-
ments, with water as the medium, that with orifices whose
areas for the combined six flutes varied between 2.3
sq. mm. and 5.3 sq. mm., the equation for the flow
was —

Where Q is the flow in gallons per hour.

« is a constant depending upon the size of the orifice.
J A. = the square root of the water head over the orifice.
0.5= the origin of the curves on the axis of x^ and is a
function of the inertia head. ♦

For all practical purposes for orifices of the dimensions

A
given above n = — , but increases slightly as the orifice

increases in size.

As showing the combination of circumstances under

feQiJATtONS FOR DISCHARGE

which any desired flow of fuel can be obtained we will
take for examples flows of i, 2, and 3 galls, per hour of
water respectively.

Taking the same formula as above, we find there is a
constant K which applies approximately for every flow
within the above limits irrespective of the head or the area,
this being 0.200 to 0.220, as will be seen from the follow-
ing table taken from the curves of flow, and this constant
multiplied by the expression a( Jk-o.s) gives the flow
in gallons per hour.

Table XLII.
Now, I Ga//. of WATER per Hour,

\lh.

Area.

X{s}h-o.sY

Inches of Water Head.

Sq. mm.

■

1-3

5-3

4-25

0.236

1.5

4.6

4.60

0.218

1-7

3-9

4.70

0.213

2.1

3-1

4-95

0.202

2.7

2.3

5-05

0.198

Flow, 2 Galls, per Hour.

2.2

5-3

9.0

0.222

2.5

4.6

9.20

0,218

3-0

3-9

9-75

0.205

3-75

10. 0

0.200

4-95

2-3

10.2

0.197

Flow, 3 Galls, per Hour.

3-05

5-3

13.5

0.222

3.6

4.6

14.3

0.210

4.3

3-9

14.8

0.203

5-4

3-1

15.2

0.197

CARBURATION

Table XLIII.
Flow^ I Gall, of PETROL per Hour^ sp. gr. 0.720, ai 55" F.

sj-h.

Area.

A(Vyi-o.5).

Inches of Water.

Sq. nun.

1.4

4.0

3.6

0.28

1.8

Z'^

4-15

0.248

2.2

2.4

4.08

0.251

3-0

1.6

4.00

a.25

3.8

1.2

3-96

0.26

FloWy 2 Galls, of Petrol per

' Hour^ sp. gr. 0.7

20, at SS" P' ■

I 7

5.6

6.73

0.296

2.2

4.8

8.15

0.245

2.5

4.0

8.00

0.25

3-0

Z-'^

8.00

0.25

4.0

2.4

8.4

0.238

/7<7Z£/, 3 Galls, of Petrol per

Hour^ sp. gr. 0. 7

20, at 55" F.

2.4

5.6

10.6

0.283

3-0

4.8

12.0

0.25

3-7

4.0

12.8

0-235

4.2

3-2

12.2

0.246

From the foregoing tables we see that within the
Hmits of experimental error it is possible to determine
the relations between fuel-flow, area of orifice, and suction
at the orifice. We further note that the liquid-flow when
petrol is used is greater than with water, in relation to
the two approximate constants 0.250 and 0.220.

The experiments upon which these calculations are
based were carried out both by means of direct fuel
heads and also by measurements made with the car-
burettor attached to an engine on the test bench. Un-

VARIOUS COMBINATIONS FOR REQUIRED DISCHARGE 9/

doubtedly further research in this direction will bring to
light many more interesting details, and time only will
enable such research to be undertaken.

There is an interesting development of this type of
orifice which is in practical use in the Brewer carburettor
which in summary gives the following results : —

When the pressure difference is 15 in. of water-head
the mean flow of petroleum spirit of 0.765 sp. gr. at 56° F.
is 0.9 gall, per hour per sq. mm. of area of orifice, with a
coefficient of discharge of 0.434.

As the pressure increases to 20 in. of water-head, the
mean flow of fuel is i gall, per hour per sq. mm., with
a coefficient of discharge of 0.440, whilst with a pressure
of 25 in. of water-head the mean flow of fuel is 1.15 gall,
per hour per sq. mm. of area of orifice when the coefficient
of discharge is 0.466.

This increasing coefficient is provided for by means of
the tubular formation round the orifice previously described.

Table XLIV. — Brewer Orifice.

The relations between area, sj h, and the constant give to a certain
flow of petrol under varying conditions.

\Jh

Ksjh

Sq. mm.

Inches of
Water.

(^= I gall, per
hour .

4-7
3-9
3-1
2.4

1-7
2.1

3-0

4.8

1-3

1-45
1.72
2.2

6.15
5-67
5-34
S.28

1.8
1.2

9.0
14.4

3-0
3-8

5-4
4-56

4.7

4.4

2.1

9.9

Q = 2 galls, per
hour . . 1

3-9
3-1

2.4

6.25

9.0

16.0

2-5

3-0
4.0

9-75

9-3

9.6

1.8

30.0

5-5

9-9

(

4-7

9.0

3-0

14. 1

Q = 3 galls, per 1
hour . . 1

3-9

3-1
2.4

13.0
19.4

33-5

3.6

4.4
5.8

14.0
136
13-9

98 '^^^^^ CARBURATION

Flow of Shell Spirit from Brewer Orifice (a) SS^F

u>l

4 8 ;

q.m.

3-9 Sq.m. >

,31 Sq.m.

U-

/ /

li-

y^^

2 35 Sq.m.

X CM

jr y^

.^^

a
lij

1-8 Sq, m.

z
o

/yy

^^^^^x

t'"^^ -^

1-2 Sq.m.

y^^,^^

0-8 sq.ms.

2 3 -"^^ 5

Square Root of Head in Inches of Water Pressure
Fig. 14.

For convenience of reference the following table gives
the area of a fluted orifice cut with a V-shaped tool of 45°
angle neglecting the rounding of the corners.

Table XLV.

Depth of Cut.
mm.

Width of Cut.
mm.

Area Through
One Orifice.

Sq. mm.

0-5

0.2

0. 10

I.O

0.42

1-5

0.62

0.93

2.0

0.83

1.65

2.5

1.05

2.61

3.0 .

1-25

3-75

3-5

1.45

5-07

I I

DISCHARGE CURVES 99

It will be seen from the above table that a tip cut of
slightly under 2 mm. deep and 0.83 mm. wide will give
the necessary area. Such a shape is not, however, used
in practice. In many instances it is preferable to allow
the depression in the instrument to increase under con-
ditions of maximum working for several reasons, the
chief of which are that a carburettor is so seldom worked
under these conditions, and it is more convenient to
fit a smaller sized instrument which is sufficient to
satisfy ordinary demands, and thus keep its cost down,
as well ^s its dimensions. Furthermore, a slight sacrifice
by doing this is really not of very great moment,
except under special circumstances, and a carburettor
of the Brewer type allows an increase of depression
without impairing the quality and uniformity of the
mixture. In passing it may be stated that by the use of
a spring the otherwise large mass of the moving part is
obviated, and this reduces the inertia of such a part.

CHAPTER VIII

SPECIAL JETS

Claudel. — This jet has been already referred to in con-
nection with the flow of fuel through small orifices, but it
should be noted that in the curves and figures of tests
with this jet, the small screw at the end of the shrouding
tube was removed. The flow curves are, therefore, only
those of a plain circular orifice, and do not apply to this
jet under working conditions.

The main feature of the Claudel jet is the shrouding
tube, which is so situated that the holes at the lower end
of it are in communication with the atmosphere in the
carburettor inlet, the effect being that when the throttle is
in a partially closed position, the actual suction operating
at the jet orifice is less than the suction in the mixing
chamber on account of the air leakage up the shrouding
tube. Furthermore, the air thus leaking issues with the
fuel stream through the upper series of holes in the tube,
thus breaking up the fuel into a fine spray. This jet is
essentially of the indirect suction type, and it is only at
full throttle opening that the absolute pressure at both
ends of the tube is approximately the same.

When the fuel stream issues from the jet orifice it is
baffled by the point of a small screw, the effect being
to restrict the surplus flow of fuel when the rate of
discharge tends to increase above the theoretical amount.
The shape of the tip of this screw is important, as also the
distance of the tip of the screw above the fuel orifice, as
the retardation depends upon the correct distance being
maintained. The author has been able to obtain very

THE CLAUDEL JET

lOI

interesting results at Brooklands with small modifications
of the jet orifice for racing purposes.

The special Claudel racing jet is a further advance in
the development of this device, as it has been found that
when a very large carburettor of this type has been fitted
to racing cars, some slight difficulties may occur in the

Fig. 15.— Claudel Jet.

ordinary way in connection with starting and slow running.
The latest Claudel racing jet is provided with a special
prolongation tube of small diameter, with a closed top
and side orifices, and is carried upwards into the throttle
barrel in contrast to projecting the whole jet into this
space in the ordinary type. Three annular fuel columns
are provided, the centre one being in communication with

I02 CARBURATION

the starting and slow running orifice, the necessary air
entering through a series of holes in the upper end of the
shrouding tube in such a manner that it issues with the
fuel stream through the centre orifice. A by-pass is pro-
vided in the throttle barrel by which the vapour passes to
the engine.

As the demand of the engine increases there is a
reversal of flow through the upper series of holes in the |
outer shroud tube, as the air then passes in the usual
manner through the lower series of holes in this tube, and
descends a second annulus in which the fuel ascends, pass-
ing with the fuel outwards through the upper series of
holes as in the ordinary Claudel jet.

As the fuel level descends in the jet, under full throttle
opening, a series of holes in the base of the inner shrouding
tube become uncovered, thus allowing a still further stream
of air to pass with the fuel up the jet. The turbulence set
up by this great rush of air, combining with that of the
main air supply, causes a very fine atomisation of the fuel.

The great problem in a racing carburettor is to so arrange
the jet that a copious supply of fuel is maintained in the
vicinity of the jet orifice whilst the throttle is closed, so
that when sudden acceleration is demanded, this fuel is
readily discharged into the mixing chamber upon opening
the throttle. This annular type of jet is so arranged that
the fuel accumulates whilst the central jet only is at work,
and is readily liberated when desired.

One other feature is interesting in connection with this
instrument, and it will be noticed that a practically true
Venturi formation is given to the passage for the gas by
reason of the taper through the throttle barrel and the
prolongation of the outlet.

Solex Jet. — The new type of jet fitted to the Solex
carburettor is also of the annular type, and is shown in
Fig. 1 6, and it will be seen that it consists of three pieces —
a centre tube with a conical seat forming the measuring
device ; a main casing containing the same, screwed into

THE SOLEX AND MILLS JETS

103

the carburettor - body ; and an outer cover attaching the
whole together in the form of a single unit. The inner
tube, as also the outer case, have each two holes pierced
in their sides near the base, those in the centre tube be-
coming uncovered by the fuel when the flow increases
under high engine suction. This drop in fuel level is due
to the hole in the base of the centre tube being smaller
than that at the top, and when the fuel level descends, an
air stream passes upwards and then downwards through
the two annular spaces, and mixes with the fuel stream
from the centre jet.

Fid. 16

Mills.

Fig. 18. — ^Javal.

Mills Jet. — This device can be fitted to many of the
standard jet carburettors, its object being to produce a
greater atomisation of the issuing stream of fuel than is
generally possible with a plain hole. Fig. 17 shows one
form of this jet whose characteristic is a spraying cone,
possible of regulation as regards the effective area between
it and a spraying nozzle, to which it is adjacent.

The nozzle closely represents that type originally used
for oil in connection with the Priestman oil engine, and
whose properties are well known. The internal conical
regulator is a convenient method of producing any desired

'^4 S^B CARBURATION

fuel-flow, as it can be screwed into any desired position
relatively to the aperture of the spraying nozzle when
the jet tube is dismounted. Once in position no further
regulation need be made, except for variations of tempera-
ture or fuel. There is no doubt as to the efficacy of such
a device when properly regulated, as the spraying properties
are great, but it must be understood that this jet is not
automatic in the sense that it has any effect upon the
efflux of fuel at any particular suction.

The Javal Jet is another type of spraying device, con-
sisting of an ordinary jet orifice fitted with a regulating
screw, upon which is superposed a spray chamber. This
chamber is fitted with a number of small metallic cylinders,
each attached to a fine wire, so that the whole resembles a
small brush. The complete outer end of the spray chamber
is filled with these metal cylinders closely packed together,
so that the fuel space is formed by the interstices between
the cylinders. It will be seen that the device is applicable
to many standard jet carburettors, and it should have a
beneficial effect upon the action of the instrument, but up
to the time of writing the author has no definite figures
upon this point.

The Holley Jet is of American design, its object being
to obtain automaticity at high suctions by means of the
admixture of air with the issuing stream of fuel.

The jet is cup-shaped, and sits in a similar formation
in the carburettor body, there being an annular space
between the jet and its container. Two holes are drilled
through the container wall, one near its base to admit the
fuel from the float chamber to the jet, and one higher up
connecting with the float chamber, but submerged under
ordinary conditions of running.

When, however, the level of the fuel in the float chamber
falls under high engine demands, the upper hole communi-
cates with the air in the float chamber, and allows a certain
proportion of that air to pass through the jet with the fuel.

The jet orifice is controlled by an adjustable needle

THE J AVAL, HOLLEY, AND STHENOS JETS

105

valve, and situated immediately above the orifice is a very
small choke tube. This tube varies in design and position
for four or six cylindered engines.

Jets with orifices in the side are exemplified by the
Sthenos (French) and Locomobile (American). The former
is shown in Fig. 20, and has two holes drilled at the
opposite ends of a diameter near the top of the jet tube.
The gradation of nozzle size is arranged by drilling, say,

Fig. 19.— HoUey.

Fig. 20. — Sthenos.

Fig. 21. —
Sthenos Jet.

two holes of the same size, the next larger orifice having
an increase of dimension to one hole only, then both holes
alike of the larger dimension, and so on.

Thus very fine gradations can be arrived at.

The Locomobile orifices are also two in number, one
being high up in the jet tube, the other lower down.

The lower hole only supplies fuel at low suctions, but
when the motor speed increases fuel issues from the upper
orifice in addition.

CHAPTER IX

MOVING PARTS

Considering the modern carburettor designs in a broad
sense, we must come to the conclusion that one of the
principal differences between the American and the
European carburettor consists in the almost general
adoption of moving parts in the American design as
distinct from their elimination in the majority of European
practice.

What the American carburettor manufacturer relies
upon is some manipulation of the air supply by means of
a suction operated valve, whereas the European designer
has a leaning towards the system of compensating jets.

This generalisation must only be considered in a broad
sense, because there are numerous exceptions on both
sides of the Atlantic. As an instance, the Holley in-
strument shows progress in the European line of thought,
in that moving parts are eliminated, and the jet orifice is
so designed that, under certain working conditions, the air
is allowed to pass through the jet orifice together with the
fuel. The flow of fuel is thus retarded when high suction
is present in the body of the instrument. As an alter-
native to the problems attendant upon high suction, we
have the school of thought which has concentrated upon
the development of a constant suction instrument depend-
ing upon a moving part in order to ensure automaticity in
action.

Moving parts controlling the degree of suction usually
have a spring-actuated or spring-balanced air valve work-
ing against a difference of pressure between the inside and

io6

FLOATING VALVES I07

the outside of the instrument, and as an alternative the
weight of the part itself may be relied upon alone.

The Brewer carburettor is a combination of both
systems, the suction being controlled both by the weight
of the moving part and by the action of a spring whose
effect can be adjusted at will. By this means the depres-
sion can be set so as to suit any particular engine.

The floating valve type of instrument has come very
much to the fore during recent years, and it depends for
its correct and satisfactory working, to a very great extent,
upon accuracy of manufacture, particularly with regard to
the dashpot and the valve stem.

Many of these instruments have given unsatisfactory
results owing to the dashpot action not being perfect, and
the immediate effect of any inaccuracy is that the floating
element flutters to such an extent that the instrument
absolutely refuses to work.

A fluttering air valve is chiefly objectionable on account
of the noise it occasions, and for this reason American
manufacturers frequently fit a leather-seated valve. When
the valve is a separate entity, and in no way directly
operates the jet, fluttering at once causes change in the
composition of the explosive mixture.

On the other hand, where the air valve controls the jet
orifice, the effect upon the mixture is not seriously marked,
and it may have the effect of agitating the mixture, and
improving its blending. For example, in one type of
carburettor any fluttering of the valve causes rapid move-
ments of the needle in the jet orifice, and assists in the
breaking up of the fuel spray. No bad effect upon the
pulling of the engine can be traced to valve fluttering with
this instrument.

An instrument of this type, in which the action of
gravity comes into play, has the following characteristics : —

{a) The inertia of the moving part due to the necessary
weight which must be put into it, particularly with the
larger sizes of instrument.

io8

CARBURATION

{b) The effect of this inertia upon the working of the
instrument as the car passes along rough or bumpy roads.

{c) The Hability to leakage of the air, or the effect of
air leakage through the joints, which will naturally alter
the depression within the mixing chamber for which the
instrument has been calculated out.

(d) The leakage of fuel at the stem of the moving part
when it is also assisting the dashpot action.

As an instance of the effect of an automatic moving
part upon the depression in the mixing chamber of a
certain instrument, the following observed values will be
of interest : —

Weight of moving part= 1.5 lbs.
Net area of part upon which suction acts = 4. i sq. in.
Calculated depression = 0.365 lb. = 9.5 in. water-head.
Engine, four cylinders, 3^^- in. x 4 J in.

. Table XLVI.

Engine Revs.

B.H.P.

Vacuum, Inches

Lift of Part

per Min.

Developed.

of Water.

in mms.

500

8.25

II. 0

2.3

1,000

19.5

9-5

1,200

23-4

10. 0

1,400

25-9

10.3

1,600

27.2

IO-75

6.5

1,800

23.8

II. 0

7-5

It will thus be seen that the moving valve regulates the
depression with very fair accuracy, at any rate sufficient for
all practical purposes.

Taking, therefore, the most usually adopted moving
part in American practice, viz., the air valve, we will con-
sider the difficulties in connection with a device of this
nature, when one attempts to carry out a theoretically
perfect carburation by means of this adjunct.

In the first place there is the inertia of the valve itself

CHARACTERISTICS OF THE FLOATING VALVE TYPE I09

to be considered, and secondly there is the spring error,
which is of necessity a feature of all spring-actuated
devices, where it is practically impossible to obtain springs
of the same nature which can be relied upon throughout
their active life.

Springs which are used in connection with air valves
are, as a rule, misused, and the more accessible they
become the more are they liable to misuse in the hands of
the driver or the owner of the car. Furthermore, it is
practically impossible on the road to give an accurate
adjustment of any spring-actuated device of this sort,
although, where the cost of fuel is immaterial, a sufficiently
satisfactory result can be, and is, obtained in ordinary
practice. There is, however, a certain period in the
working of an instrument, viz., when the extra air valve
begins to lift, where carburation is bound to be upset
momentarily, due to the very great difference of prevailing
conditions when the said valve operates or not, the effect
of its lifting being a reduction in the vacuum within the
mixing chamber.

In order to reduce the variation of vacuum at such a
time to its minimum amount, two springs of different
strength are sometimes employed, the lighter one coming
into operation at the initial stages of the valve movement,
its resistance being supplemented by that of a stronger
spring as the valve lifts from its seat a further amount
when the suction of the engine becomes greater.

The author, in designing his carburettor, has obtained a
somewhat similar effect to the two-spring arrangement by
utilising the weight of the moving valve to overcome the
initial or low suction, so that the spring action is in reality
operative over a short portion only of the valve's lift.
Furthermore, on account of the design of the fuel orifice
giving at all working suctions a flow of fuel proportional
to the square root of the depression, any spring error is
negligible for ordinary purposes.

In such a device the valve movement, to give full open-

CARBURATION

ing, should be small, so as to still further eliminate errors
due to variations in the shape of the air orifice.

Whilst considering moving parts whose effect is upon
the constituents of the explosive mixture, the modulating
pin must not be overlooked. As this important detail has
been dealt with in previous chapters, we will only briefly
refer to it here.

Such a part, subject to frequent changes of position rela-
tively to the orifice in which it works, should be so designed
that it does not suffer from wear, and it, therefore, should not
be allowed to hang against the side of the fuel orifice.

This pin, together with the air valve, can be controlled
by the same dashpot, and this may take several forms in
actual practice.

At one time mercury was adopted as a suitable medium
for damping out vibrations or oscillations of the moving
parts, but this substance is expensive and heavy, and is
liable to oxidise and cause trouble.

Nowadays pistons, either working in an air cylinder
with a restricted orifice communicating with the atmos-
phere are used, or pistons in a fuel chamber. Wherever
we have a piston of the ordinary sliding type, accuracy
of fit is a sine qua non — if the fit is bad the piston is
useless as a dashpot, if it is tight it restricts the movement
of the parts.

A dashpot is primarily a device for damping out
oscillations with as little friction as possible ; and where,
as in the Scott-Robinson carburettor, a large piston is
employed, a very small hole is drilled in the dashpot cover
or piston so as to restrict the air flow into or out of the
cylinder as the piston commences to descend or otherwise.

In this case tightness of the piston is obtained by a
series of hydraulic grooves round the circumference of
the piston, and the friction is small, as the amount of air
passing through the hole is small.

The Stewart precision carburettor relies for its dashpot
action upon a prolongation of the air valve stem which

DASHPOTS 1 1 1

works in a containing cylinder in communication with the
fuel in the float chamber. The communicating hole is small,
so that as long as the fuel does not creep up the stem it is
forced backwards and forwards between the float chamber
and the dashpot cylinder as the valve rises and falls.

The Polyrhoe dashpot is of the large air cylinder type,
and in this case the operating spring is contained in the
dashpot ; and on account of the size of the spring this
dashpot is of somewhat large dimensions.

Linked up with the question of dashpots and their I
need is that of inertia. '

We will repeat the definition of the word inertia, so that
it will not be necessary to refer to another chapter.

Inertia is that property of a body by virtue of which
it tends to continue in a state of rest or motion in which
it may be placed, until acted upon by some force.

Thus we see that a free moving air valve is subjected
to continual forces of varying magnitude and periodicity
on account of engine suction. The force acting is the
atmospheric pressure tending to raise the valve from its
seat, and the inertia of the valve is a function of its mass.
When once the valve has started lifting, its tendency is
to continue so doing on account of the velocity in a
vertical direction, imparted by the impressed force. The

valve has attained a momentum — at the end of time

t, and this momentum must be damped out. Were an
engine working at a constant load and speed the whole
time, the question of inertia would not come in ; but as
this is not the case, we will see what its effect is.

In the first place, where the valve has considerable
mass, it is quite possible that the engine suction will
increase above the normal before the valve rises from its
seat and admits more air. Under these conditions the
mixture will tend to become rich. For this reason a
light moving part is desirable.

If the range of possible working is great, the valve may

112

CARBURATION

attain considerable velocity in a very short period of time
after it has commenced to lift, and as the momentum is
dependent upon the square of the velocity, the possible
range of working should be small. With a spring-con-
trolled valve, the effect of the spring increases as its
compression, so that the spring itself brings the valve to
rest before it has attained a seriously high velocity.

The valve is accelerated from rest to a certain velocity
V = FX/, where V is the velocity, F = the acceleration, and
/ the time during which the acceleration acts.

When the throttle is quickly closed the valve still
tends to remain in its position of lift, and is only returned
to its seat by the action of gravity, supplemented or not
by that of a spring. A spring, therefore, is useful as before-
mentioned on account of its displacement being propor-
tional to the pressure exerted. This pressure at once
assists in returning the valve against its inertia property.

There is another condition under which the inertia of a
valve may be detrimental to good working, namely, when
the car traverses a bumpy road. It is here where a dash-
pot action should be as perfect as possible for carburettors
whose jets do not proportion correctly. Rapid vertical
accelerations to the car tend to cause the air valve to flop
up and down.

What is termed " pick up " has become an important
feature of modern design, and in a carburettor fitted with a
moving part, the inertia of that part has a very important
bearing upon this quality.

If the weight of the part is great, there is a tendency to
lag when the throttle is suddenly opened. This is a good
feature, perhaps, for ordinary driving, as it allows the
engine to attain its power gradually. There is a class of
user, unfortunately, who expects the engine to jump away
so soon as the throttle is opened, and for his benefit there
should be no appreciable lag in the carburettor action.

In the first place, the engine revolutions must increase
to a certain amount before the necessary suction is obtained ;

THROTTLES ll3

and secondly, that suction must be allowed to operate for
an appreciable time before the valve commences to lift by-
overcoming its inertia.

Throttles. — There is one other moving part to which
brief reference will be made before passing on, and that is
the throttle.

Three outstanding shapes of throttle are found at the
present time — the barrel or sleeve, the butterfly, and the
valve. Taking these in turn, it is generally found that the
barrel throttle is adopted on the " single lever control "
instrument, where it commands the air supply as well as
the vapour, as in the Claudel Hobson. This type of
throttle forms an important integral part in the design of
the carburettor, and its parts should be correctly shaped to
enable the carburettor as a whole to function properly and
give the correct degree of suction at the jet orifice.

A barrel throttle must be a proper working fit in the
carburettor body, both as regards its circumferential surface
and that of its ends and trunnions, otherwise air leakage will
be set up. This type of throttle has large working areas of
contact, which should be kept free from scoring, and par-
ticles of dirt should be excluded, as these will either cause the
throttle to stick or will produce scoring of the surfaces.

Some barrel throttles are so arranged that they bring
into operation two or more fuel jets in sequence, so that as
they are rotated, specially shaped air ports allow the air to
be drawn through the choke tubes surrounding the said
jets. In other cases a barrel throttle is sometimes arranged
so that at the end of its limit of working communication
is made with the outside air, thus enabling a supple-
mentary air supply to be drawn into the cylinders at
periods of high engine speed. On the other hand, this
communication with the air may be made by overrunning
the closed position of the throttle, so that air alone can
pass into the cylinders when descending a hill.

Some emphasis is given by certain designers to the
necessity of giving a uniform progressive throttle opening
as the actuating lever is operated, but the author attaches
8

114

CARBURATION

no importance to this property. The reason is that foot
control is now so universal that the driver instinctively
depresses his pedal in accordance with the performance of
his engine. It is, however, important that the first few
degrees of lever movement do not cause the engine to race
away, otherwise there may be some difficulty in making
the slow running adjustment.

Sleeve throttles are generally similar in their arrange-
ment and function to the barrel, excepting that the trun-
nions are dispensed with, and the movement is longitudinal
instead of rotary. The necessity for tightness and the ex-
clusion of dirt still remains.

The butterfly is the simplest form of throttle to make,
and this, the original type, has entered upon a new lease of
popularity with the introduction of the weight or suction
operated carburettors. On the other hand, the butterfly is
almost universally employed in American practice with all
types of instruments, probably as this class of throttle is
cheap and easy to make, and does not rapidly become
deranged even under the worst conditions of dust and dirt.

The butterfly should be of substantial design, as it is
essentially a means of holding up the suction of the engine
and regulating the extent of the effect of this suction upon
the mixing chamber of the carburettor. Furthermore, the
trunnions upon which the butterfly works should be of
ample dimensions, having a large bearing surface, so as to
prevent air leakage and maintain the throttle in its correct
position. A butterfly in its closed position should not be
normal to the bore of the tube in which it works, on
account of the turbulence which it sets up ; preferably it
should, when closed, be at a good inclination, so that small
movements of the lever only are required to produce
full throttle opening.

The trunnions can conveniently be made to work in
detachable bearings, screwed into the body of the instru-
ment, to provide ready means of renewal, and the bearing
remote from the actuating lever is better formed with a
closed end, so that air leakage is positively prevented.

THROTTLES

115

A typical butterfly throttle of advanced design is
shown in Fig. 22.

The valve throttle is employed in some cases on the
score of its ease of correct fitting, and owing to the fact
that it can readily be seated and kept tight. Such a
throttle is similar to the ordinary mushroom valves, fitted
to a poppet valve engine ; but one point must be borne in
mind in considering the application of such a throttle in
particular, and that is the deflection of the vapour stream.

Fh;. 22. — Butterfly Throttle of Advanced Design.

As previously pointed out, obstructions are to be avoided
as much as possible, so any type of throttle should, when full
open, at any rate, cause as little direct obstruction, particu-
larly by normal surfaces. The valve can, of course, be suit-
ably designed with this object in view, but care is required.
A valve throttle should not suffer from wear, and its
actuating mechanism can be so arranged that there is no
direct communication between the mixing chamber and
the external atmosphere, even if any parts do wear. This
is a point in its favour.

CHAPTER X
FLOAT CHAMBERS

Every modern carburettor is fitted with a float chamber,
the duty of which is to maintain a constant level of fuel
in the instrument itself, and this device has been almost
universally adopted ever since the celebrated Maybach
patents were fought out in the law courts.

It is quite possible, however, to eliminate the float
chamber, and several attempts in this direction have been
made with more or less success, but as a commercial pro-
position many difficulties occur when the elimination exists.
In the first place, the variation of fuel head in the tank is
difficult to compensate for unless a sudsidiary tank is pro-
vided, fitted with some means of regulating the flow of fuel
to this subsidiary tank as the jet allows fuel in measured
quantities to pass through to the engine. The ordinary
float chamber can be operated in many ways, and several
examples are shown in the following figures.

The first important point to bear in mind in designing
a float chamber arrangement is, that the chamber itself
should have sufficient capacity in order to prevent the
engine stopping under abnormal conditions, or when the
fuel is not flowing regularly to the float chamber. Secondly,
the area through the needle valve which supplies the float
chamber must be of sufficient size to pass the necessary
amount of fuel, even when the tank is almost empty and
the fuel head is low.

In several designs of carburettors, difficulties have been
experienced in getting the fuel into the float chamber, due
to the needle valve being too small, and it must be borne

ii6

METHODS OF OPERATING FLOAT VALVES II7

in mind that the area through this valve should be con-
siderably larger than the area of the jet orifice. In cases
where the fuel needle is situated above the float, the fuel,
on issuing from the needle valve, strikes on the top of the
float. When the fuel issues at high velocity the pressure
due to the velocity of the fuel acts upon the float — the
issuing stream striking on the top of the float will tend to
prevent it rising, and thus will, in some instances, cause the
carburettor float chamber to flood. In cases where the
float is supported, as in common American practice, from a
hinge at one side, the effect of the issuing stream upon the
float is very small, as the moment of the pressure about
the fulcrum from which the float swings is a very small
one, and therefore its effect upon the float is negligible.

It is probably unnecessary to point out that the action
of a carburettor float is similar to that taking place in the
ordinary domestic water cistern fitted with a ball valve,
and the float performs the same function as the ball itself,
through the medium of levers, or by direct connection, and
closes the fuel inlet valve when the level is at a pre-
determined height.

In the working of a carburettor it may happen that, on
account of high engine suction, the level of the fuel in the
float chamber does not stand at the same height as the
rest level, and it has been thought in the past that the
deviation from the true level had a serious effect upon
the operation of a carburettor jet.

The author considers that this is a fallacy.

If one comes to consider the small deviation that is
possible in the float chamber as related to the total
depression, or difference of pressure, between that of the
mixing chamber and the float chamber, it will be seen that
the proportionate discrepancy in the level bears a very
small relation to the total depression. For example, it
may occur that the depression in the mixing chamber is
of the order of from 10 in. to 15 in. of water-head,
whilst the error in depression in the float chamber will

ii8

CARBURATION

only amount to a fraction of an inch, which is quite
negligible. There is another point upon which the author
takes the opportunity of expressing an opinion, and that
is with regard to the necessity of fitting an air vent hole
in the top of the float chamber. Owing to the difficulty
experienced in some cases in getting sufficient fuel to pass
through the needle valve of the float chamber, the author
considers that it is advisable not to use a vent hole in this
chamber, and to allow the suction upon the jet to facilitate
or accelerate the flow of fuel through the float chamber
needle valve. When there is no vent hole in the float
chamber, this suction of course comes into operation,
whereas when a vent hole is employed, the only difference
of pressure which is effective is the difference of pressure
due to the head of the fuel in the tank, above the needle
valve of the float chamber.

The author has found no difficulties in practice on
account of the elimination of a vent hole, but in some cases
flooding may result.

Now, with reference to the float itself, some authorities
consider that it should be a fairly close fit in the float
chamber, as the proximity of its walls to those of the float
chamber would assist in locating the float, and prevent it
moving about. Messrs Gillett and Lehmann carried this
idea still further in shaping their float as a double cone,
with the object, in the first place, of retaining a large bulk
of petrol in the float chamber ; and secondly, to guide the
float itself, as the large ends of the double coned float were
of almost the same diameter as the float chamber, thus
steadying the float within the chamber. Such a shape of
float is also very sensible to movement, but is largely self-
damping, on account of the resistance given by the conoidal
surfaces to movement in a vertical direction. This type
of float, in actual practice, was arranged to rest upon
a pair of small balance levers in the ordinary way, with
a central weighted fuel needle having its seating down-
wards.

THE SHAPE OF THE FLOAT II9

With further reference to the shape of the float, it is
important to bear in mind that in cases of hollow brass
floats, which are so frequently adopted in ordinary practice,
there may be difficulties arising due to the difference be-
tween the internal and external pressure to which the float
is subjected, and for this reason the ends of the float should
not be flat, but should certainly be dished or corrugated to
allow for slight expansions and contractions of the air
enclosed within the float. Unless these precautions are
taken, leakage is very liable to set up on account of the
working at the soldered joints.

In the construction of floats of this type it is well
to eliminate as far as possible all joints, and a suitable
float can be made from two pressings soldered together
with one circumferential seam. These pressings or stamp-
ings must naturally have more seams than one, in cases
where the needle passes through the centre of the float,
or when a passage is provided for the jet, as in the con-
centric type of instrument. In any case, however, care
should be taken in the design so that the number of
soldered joints can be reduced to a minimum.

Modern practice, particularly in America, is quite in
favour of the cork float, but it is advisable that when such
a float is used, it be built up of a large number of layers
of cork to prevent warping. Six layers form a convenient
number, and in many instances the cork is treated with
shellac, and baked at least twice before being fitted into
the float chamber. This is done to prevent the cork
becoming sodden in use.

There are many methods by which the float actuates
the valve, and it may be attached directly thereto, so that
when the float lifts, the valve is drawn up on to a seat. On
the other hand, the float may only have a small amount of
buoyancy, sufficient to take its own weight from a needle
which is pressed, or drawn up, on to its seat by means
of a spring (Fig. 24).

The converse of such an arrangement is the downward

120

CARBURATION

seated needle, where the needle seat is at the bottom of the
float chamber, and the needle is of sufficient weight to seat
itself when any counteracting pressure is relieved from it.
In such a case the float operates through the medium of
toggle levers, and as the float rests upon these toggle
levers they in turn raise the needle from its seat (Fig. 25).
Similar arrangements to those described are in some
instances fitted to the top of the float chamber, but it is
immaterial, generally, where these fittings are placed, so
long as sufficient pressure is allowed to act upon the
needle valve in order to keep it petrol tight (Fig. 26).

Fig. 23.

Fig. 24

In passing it may be pointed out that unless a conical
seated needle is true, and is prevented from rattling or
shaking, it is often liable to leak. In practice it is some-
what difficult to get the needle tight, unless grinding is
resorted to, due to inaccuracies in drilling the various holes
through which the needle passes in a perfectly true line.
For this reason a spherical seat is preferable, as it allows
a slight movement to take place without causing the
needle to leak.

In the Brewer carburettor the conical needle has been
abandoned in favour of the spherical seated needle, which
has been found to work very satisfactorily under all
ordinary conditions (Fig. 31, p. 163).

ARRANGEMENT OF THE FLOAT CHAMBER

121

There is one other point which should receive attention
before leaving the subject of the float chamber, and that
is the position of the float chamber relatively to the mixing
chamber.

It has been the general practice in the past to make
the float chamber on a different centre line to the mixing
chamber, and the two situated side by side. When the
carburettor is placed in position on the car, the float
chamber may be either at one side of the mixing chamber,
or in front of it, or behind it. There is a certain amount
of importance attached to the position of a float chamber

Fig. 25.

Fig. 26.

which is not on the same centre line as the jet, as it will be
seen that, as the car ascends a hill, when the float chamber
is in front of the mixing chamber, the tendency is for the
jet to receive rather more than its normal supply of fuel,
which is convenient. Conversely, on descending a hill, the
inclination of the car retards the flow of fuel by reason of
the difference of the two levels. When, however, the float
chamber is placed to the rear of the mixing chamber, the
reverse takes place, which is a scarcely desirable feature.*

Probably the best arrangement is the concentric system,
where the float chamber is below, and the float itself
surrounds the jet, as in this case the relations between

* The reader is referred to remarks on p. 117, lust paragraph.

122

CARBURATION

the level of fuel in the float chamber and in the jet
orifice are always the same. Furthermore, it makes a
very convenient manufacturing proposition, and the car-
burettor generally is of much smaller dimensions than
when a separate float chamber is employed.

The concentric arrangement reduces to a minimum
the length of the fuel passage to the jet, and consequently
inertia effects are reduced in the fuel stream.

A concentric carburettor lends itself to universal fitting,
as by a simple means the air and fuel openings can be
set in any desired position relatively to one another.

An important point arises in the attachment of the
fuel pipe to the float chamber, and it should be such that
the bulk of the vital parts of the carburettor, such as the
float and needle valve, also the jet, can be removed without
disconnecting the fuel union.

CHAPTER XI

PETROL SUBSTITUTES

Owing to the high price of petroleum spirit, and the
tendency of this price to increase, a considerable outcry
has arisen and attention been turned to fuels other than
those usually adopted. It is outside the sphere of this
book to deal fully with the question of possible motor fuels,
but this opportunity is taken to remind the reader that
there are no great or special difficulties connected with the
use of alternative fuels. The wisdom of doing so, however,
is another matter, and it is evident that so long as the
source of the substitute is the same as that of petroleum
spirit, and so long as the same groups of financiers control
the substitute as the present fuel, difficulty and doubt will
always arise as to the practicability of adopting that sub-
stitute with any financial saving.

However, if a greater proportion of the crude can be
used for motor vehicles than at present, it would be logical
to suppose that a reduction in price of the all-round fuel
should ensue. Thus, supposing that instead of, say, 15 per
cent, of the crude, as at present, we could use 30 per cent,
by suitable treatment, the average price would be the
mean between that of the lighter distillate and that of the
heavier, plus the cost of treatment.

The treatment of hydrocarbon liquid fuels is no new
thing, and generally consists in precipitation of the un-
saturated hydrocarbons contained in the fuel by means of
certain acids.

Cracking is resorted to in order to increase the yield of
the lighter hydrocarbons from the crude, and by this means

<33

124 CARBURATION ^"^

volatile spirit can be produced from the heavier hydro-
carbons. In this way it is possible to break down
petroleum of a high boiling point to an oil of a lower
boiling point and an increased yield of the lighter products
is obtained.

Mr Horatio Ballantyne, the well-known chemist, states
that if one proposed to start with an oil having the ap-
proximate formula C^3H28, and to reduce it to, say, heptane,
having the formula QH^g, it would be necessary to
increase the proportion of hydrogen relatively to the
carbon. However, no practical means are known to
chemistry whereby this can be done, but by a simple
cracking of the oil, volatile mixtures of paraffins, un-
saturated hydrocarbons such as olefines and benzene and
its homologues, might be arrived at.

In the production of light oils, such as petrol, it is
difficult to conduct the breaking down of the heavier oils
without producing carbon and large proportions of per-
manent gases, such as methane, CH^, and hydrogen. The
most likely method of cracking oil for the purpose of
obtaining spirit without such risk would therefore appear
to be by means of distillation under high pressure, so
that the temperature can thereby be more carefully
regulated.

Liquid fuel has from time to time been treated by the
addition of picric acid and by various gases, but such
practices are not to be recommended. In the first place,
petroleum spirit will not contain any appreciable pro-
portion of the former in solution, and with the latter the
involuntary liberation of the gases causes trouble in the jet.

The weight of gases which is soluble in petrol is very
small, and even in the case of acetylene only 0.15 per cent,
by weight can be contained in solution.

Mr Ballantyne states that " when the carburation is
such as to give a mixture of petrol and air in about the
theoretical proportions, acetylene does not act beneficially,
and the greater sensitiveness of the acetylene tends to

TREATMENT OF FUEL 1 25

cause pre-ignition. In the case of petroleum products of
less volatility than petrol, treatment with gases leads to no
improvement."

With reference to mixtures of liquid fuels, such as
paraffin, petroleum spirit, benzol, and alcohol, experiments
have been carried out for many years by the author and
others, and it is notable how the admixture of certain pro-
portions of a volatile liquid with one which is less volatile
enables the latter fuel to be burnt in the engine cylinders.
The obvious reason for this fact is that when a sufficient
disintegration of the fuel takes place at the carburettor jet,
and provided that the velocity of the fuel through the
carburettor and inlet pipe is maintained, the heavier
particles of the composite fuel are held in suspension in
the incoming charge and ignited in their liquid state in the
cylinders.

When using such a fuel it is therefore obvious that the
remarks in a previous chapter on capacious inlet manifolds
do not hold good, for the temperature of the walls due to
the proximity of the circulating water is never sufficiently
high to evaporate any precipitated particles of fuel.

Care must also be exercised, in consideration of the
capacious manifold argument, that the nature of the fuel
is taken into account, for the heavier fractions of ordinary
motor spirit only boil between 130° C. and 150° C, whereas
the temperature of the manifold is never as high as 100° C.
A mixed fuel can be detected by analysis.

Alcohol, for instance, is soluble in water, and can be
separated by the addition of water to the mixed fuel. The
alcohol will dissolve, and the proportion of the remaining
fuel which floats on the top can be measured.

Mr Ballantyne gives a nitration test for the detection
of benzene (benzol).

To 25 c.c. of nitric acid (sp. gr. 1.42) add carefully
25 c.c. of concentrated sulphuric acid, and cool the mixture
to about 20° C. to 30° C.

Add 25 c.c. of the sample gradually, and with constant

126

CARBURATION

agitation, taking care not to allow the temperature to
exceed 50° C.

If benzene is present, the odour of nitro-benzene will be
noted.

Keep the mixture at a temperature of about 60" C. for
half an hour with frequent agitation ; pour the whole into a
separating funnel.

The waste acids can now be tapped off from below the
upper layer of petrol and nitro-benzene. Now add nitric
acid of sp. gr. 1.5, sufficient in quantity to dissolve the
nitro-benzene, and the solution can be tapped off from
below the layer of petrol, which can now be measured.

The acid solution should be poured into, and well
agitated with, five or six times its volume of water, and the
nitro-benzene is thus thrown out of solution, and can be
measured.

The observed volume of nitro-benzene, multiplied by ,;
0.85, gives the correct volume of benzene. '^H

The author has conducted a number of tests with '
mixed fuels specially treated in order to determine the
best proportions of the various constituents for all-round
work.

In carrying out these tests it was primarily set down as
a sine qua non that an ordinary standard carburettor should
be used, without making adjustments of any sort, and that
the car and engine should be changed over from one fuel
to another as desired.

The principal points noted were : —

Ease of starting.
Acceleration.

Power on inclines or falling off in speed.
Maximum speed obtainable on the track.
Consumption.
Slow running.

Behaviour under rapid changes of throttle
opening.

TESTS WITH MIXED FUELS

127

pc-i

Mean Accelera-
tion to 30 Miles
per Hour — Feet
per Sec. per Sec.

10 0 r^ 10 10

-^ ; fOvO '^ -^ "^ ; -^ ON

d " d d d d d do

. CO .

00 . CO .

00 ; ON ;

6 ' 6 '

• 3

10 10 r^ 10 in

On u-^ ro •"" fOOO m CO 00 O
00 VO 00 00 t^ t^CO lO t^CO

6666666666

ro
1000 OS

ON t^ 10

d d d

in in

CO in r^ "^

6 6 6 6

<~i ON invo
0 vo ON in

>-^ 6 6 6

B.H.P.
Hour.

10 10 vo 0

rh r^vo ■^ ro 0 in 10 « ro
HHOOOOaNOOr-OO

to 0 ^
0 0 r-

mOwmOmh-iOmm

M M 0

t-H

iot^ioio>oiomO 10 Cn^ >j^ I-'

►H CO in 0

■4- to to to

M CO HH ro

rO N ^O ^O fO to toco to "^

l-lfOHHI-ll-IMI-lfO»-IM

10 ro On
N M CO

B.H.P.
at Road
Wheels.

10 10 10 vo 10 10 lovo lo^o
6^660666^6-^

MMHHMl-ll-HMMI-IM

tJ- m in

rj d d
ri M fO

0 ^ U-) 0
M in d 10

M N M N

10 m

r^ 0 to

q "^ 0 in

N CO Tt N
N M N N

Ot^ONNNH-(ONO

in ti >0

M M M

Consump-
tion— Pints
per Hour.

rl- N OnOO 10 0 rO^ O

n in N

M t^ d "^

M M M M

nmmOOQi-iNOM

to 0 to

N M M

Speed,
M.P.H.

vO *^ vo 00 10 ro M
d fO 0 0 r^od ds t^ On HH
rO'Tj-rorON N w ■^ri rO

i~^ to to
in Onco*

invo 0 0

1^ 6 6 6

to tJ- to -^

Specific
Gravity
at 57° F.

10 m m^ ^ vo vO 'O VO

in in

0000

10 inoo 00

t^ t^co 00

6 6 6 6

000000000

0 0

Fuel.

1 1 1 ■ 1 1 1 1 1 1 1 1 1

■' ^.^^-QJo;

N f^i CO tJ- irjvo 00 00 ON M t-" ^_ _

d6dddddddo6_^_^
;z; Z Z iz; ;2; :2; iz; iz; :z; 12; ;z; c^ c^

Shell crown -
Shell crown -
Benzol
Benzol

128

CARBURATION

The various fuels were tested in the author's car, which
is conveniently adapted for such work. Elimination of the
undesirables has only taken place up to the time of writing,
but as these varied in only minor degrees with regard
to their constituents from the best fuel, the different
behaviours will be of interest. The two carburettors used
were, first, a Claudel Hobson of 26 mm. diameter, and a
Brewer carburettor of nominal 1 in., which was, however,
never fully opened up.

The remainder of the tests with the fuels in this
carburettor were carried out on the road, so that the results
are not comparable.

The car loaded weighed 1.5 tons, and had a rolling
resistance of 130 lbs. on the track at 30 miles per hour,
and 210 lbs. at 43.7 miles per hour, and 236 lbs. at 47 miles
per hour.

A wide wind-screen was in use during these tests, but
the weather was calm each day.

Benzol. — The carburation of benzol requires no special
apparatus, and is attended with no difficulties. This fuel
can be used with any good carburettor without alteration,
as has been proved for years past. The author conducted
a number of experiments in the years 1905-6 with benzol,
which then cost about eightpence per gallon at the gas
works, and he showed that the saving which could be
effected was proportional to the relative prices of benzol
and petrol, plus about 12 to 20 per cent, in favour of benzol.
This is no doubt due to the greater specific gravity of the
benzol, i.e., about 0,880 to 0.885 as compared with petrol at
0.715, and therefore to the greater weight of benzol in one
gallon, the standard unit of sale retail.

Benzol, as we all know, is a distillate of coal tar, whose
formula is CgHg, and contains about 163,680 B.Th.U. per
gallon, as compared with about 157,000 B.Th.U. in the case
of petrol, or taken by weight about 20,000 B.Th.U. for
petrol per pound.

The total evaporation or boiling point of crude benzol

BENZOL t2g

is 145° C. or 293" F., and it has an explosive range of 2.7
to 6.3 per cent.

Crude benzol is not, however, suitable for motor car
work, and it is, therefore, washed or purified for this purpose,
chiefly in order to eliminate certain sulphur compounds
which are contained in solution.

Pure benzol boils at about 80° Cor 176 F., but com-
mercial 90 per cent, benzol is more usually met with, and
90 per cent, of this hydrocarbon liquid evaporates in a
retort at 100° C. 90 per cent, benzol consists of the follow-
ing combinations, whose proportions vary between 70 to
75 per cent, benzene, 24 to 29 per cent, toluene, and 17 per
cent, xylene, but in some cases the benzene may be as high
as 80 per cent, and the toluene as low as 14 per cent.

The presence of toluene is desirable on account of its
lower freezing point, as pure benzol will freeze at a tempera-
ture of 42" F., whereas, when a considerable proportion of
toluene is in the product, the freezing point drops to 5° F.

The production of crude benzol at the gasworks from
I ton of coal distilled is at present about 2I- galls., and
its bulk is reduced by 25 per cent, in rendering it suitable
for motor car purposes, this yield depending upon the
amount of gas distilled per ton of coal, and may be as high
as 9 galls, per ton of coal when 7,000 cub. ft. of gas only
are distilled.

The sulphur compounds in benzol are washed out to a
great extent by means of sulphuric acid, as these amount
to about 150 grains per gallon, and are easily discernible
by their smell. The process of washing and refining costs
a penny to twopence per gallon. In 90 per cent, benzol
there remains from 75 to 90 grains per gallon of carbon,
bisulphide, and other compounds.

The difficulty about benzol, from the motorist's point of
view, is that he cannot easily obtain it, and furthermore, is
not likely to do so in any quantity for some time on
account of the large export trade, particularly with France.
The absence of duty on benzol into France, and the prefer-

150 ^^^^^^ CARBURATION

ential local octroi into Paris make benzol an attractive fuel
in the French capital, so that the refiners of benzol in
England find a ready and profitable market in that
country.

The fuel question is too deep a one to go into fully
here, and is more dependent upon finance than upon
engineering possibilities ; but suffice it to say that, were
benzol procurable in reasonable quantities, it could form a
serious rival to petrol. As far as we can see at present,
there is, however, no reasonable hope that the yield of
benzol from gasworks could ease the fuel situation appreci-
ably.

Benzol is also produced in the manufacture of coke for
metallurgical purposes, and at the present time lo to 12
million gallons are produced per annum in England in
this way, and the yield may be as high as 14 galls, per
ton of coal carbonised.

If modern recovery plants were utilised in every works
where the manufacture of coke is carried on, it would be
possible to increase this yield to 30 million gallons of
benzol per annum. The price of benzol is in a great
measure governed by the price of petrol, and at the time
of writing is about one shilling per gallon in bulk at the
works ; a few years ago it was half this price.

As far as the physical properties of benzol are con-
cerned, M. Edmund Ledoux gives the calorific value of
benzol as 8,844 major calories per litre, as against 7,910 for
petrol, showing a favour of 12 per cent, for benzol.

The heat required to vaporise a quantity of liquid
of each, containing 1,000 calories of heat, is —

Benzol = 12.9 calories = 1.29 per cent. ] of the total heat of com-
Petrol =14.1 „ =1.41 „ J bustion.

From the above figures 89.3 volumes of benzol contain
the same quantity of heat as 100 volumes of petrol.

It will be seen that a smaller volume of benzol is
required than that of petrol to carburate a given quantity

VISCOSITY OF BENZOL

131

of air, but it is found that the viscosity of benzol is greater
than that of petrol, almost in the exact ratio of the
required reduction of volume of fuel shown by the above
figures.

Table XLVIII. — Times taken for 2 oz. of Liquid Fuel at

55° F. TO FLOW THROUGH AN OrIFICE O.95 MM. DiAMETER.

Fuel.

Head over Orifice corrected for equal pressures
in mms.

"Anglo 0.760"

Benzol - - - -

sec.

77
116

sec.

106

sec.
80

Table XLIX. — Times taken for 2 oz. of Liquid Fuel at

55° F. TO flow THROUGH AN OrIFICE 1.2 MM. DiAMETER.

Fuel.

Specific
Gravity.

Equivalent Head for
Petrol — 120 mm.
Benzol — 99 mm.

Head for
Petrol ==150 mm.
Benzol = i24mm.

Head for
Petrol — 1 80 mm.
Benaol = i48mm.

"Anglo 0.760"
Benzol

0.730
0.885

sec.
62

sec.

35
37

sec.
30

Table L. — Quantities of Benzol (sp. or. 0.875) blowing
THROUGH Orifices in Gallons per Hour. Tempera-
ture, 66° F.

Diameter of Orifice

Fuel Head=i2o mm.

150

180

in mm.

Equivalent Water-Head -105 mm.

131

157

Gal.

I.O

0-775

0.94

1.07

1.2

1. 21

1.36

1-55

1.4

1.83

2.06

2.25

132

CARBURATION

Table LI. — Quantities of Benzol (sp. gr. 0.875)
THROUGH Orifices in Litres per Hour,
TURE, 66° F.

flowing
Tempera-

Diameter of Orifice
in mm.

Fuel Head = 120 mm.
Equivalent Water-Head = 105 mm.

150
131

180
157

1.0
1.2
1.4

Litres.
3-52

5-5
8.32

Litres.

4.27

6.18

9-31

Litres.
4.86
7.04
10.22

The reason why two figures are given for the head in
each instance in the above table is that in a carburating
system all readings are taken in water-head, the depression
at the jet orifice is reckoned in inches or mms. water-head,
and this reckoning must not be confused with the theory
of hydraulics, where the acting head of the liquid is the
basis.

Paraffin. — This distillate from the petroleum series has
probably been used to a greater extent than any other, and
principally for domestic purposes and for use in internal
combustion engines. As soon as the gas engine became a
commercial possibility attention was turned to the use of
oil, and the oil engine progressed simultaneously with the
gas engine.

Carburation, in the broad sense of the word, covers any
means of intermingling hydrocarbon with air in suitable
proportions to form a combustible mixture, and the conver-
sions of solid coal into gas is at the lower end of the series,
which at its upper end consists in the evaporation at
ordinary temperatures of a light benzene.

If one considers the question in this manner, it will be
obvious that as one progresses along the whole series the
various fuels to be treated require greater additions of heat
in order to effect carburation as the particular fuel
approaches the end of the scale of fuels which terminate^
with coal.

PARAFFIN 133

We will not consider here any fuel more difficult to
carburate than paraffin, as from the automobile point of
view, fuels with higher boiling points and more difficult of
treatment are scarcely within the range of possibility at
the moment.

The advent of the Diesel engine, followed by other
types of engines in which the fuel is directly injected into
the cylinders, has rather detracted from the lines of pro-
gress in systems of using paraffin, either in its liquid or
gaseous form, and in this form admitted to the engine
during the suction stroke. This latter has for more than
twenty-five years been the method adopted for utilising oil
in the cylinders of stationary internal combustion engines,
and naturally during that time certain fixed methods have
been employed for suitably dealing with such a fuel.

Two distinct systems exist for carburetting air by means
of a liquid fuel whose boiling point is above 150° C, and
these are as follows : —

I. As paraffin or kerosene without chemical change,
either in an atomised, or partly atomised and partly
vaporised state. 2. With chemical change such that the
paraffin before entering the cylinder has been wholly or
partly decomposed into the lighter hydrocarbons.

The first method was adopted in the early Priestman
engine, and a spray producer of special form was fitted
into the end of a cylinder in such a manner that the fuel
was injected into a hot combustion chamber in the form of
spray, and there more or less decomposed, at any rate suffi-
ciently to form a combustible mixture. When such a
method is attempted in connection with a modern auto-
mobile engine, and a spraying device is used to supply a
number of cylinders, there is always the liability for the
suspended particles of fuel to deposit as a liquid in the
induction pipe unless the atomisation takes place in close
proximity to the cylinders.

This deposition of liquid is naturally aggravated by
any bends or obstructions to the passage of the fuel on its

134

CARBURATION

way from the atomising device to the engine cylinders, and
for this reason alone it is practically impossible to rely
upon an external atomiser alone for the carburation of air
by means of paraffin.

Under the second series we have a different state of
affairs, and an attempt is here made to produce an oil gas
such as is well known in the Manfield process. If we are
using a fuel which evaporates completely between 1 50°
and 3c>o° C, and that fuel is submitted to a temperature at
least equal to that of the boiling p")int of its heaviest
fraction, we shall produce an oil gas which is more or less
fixed.

When we have such a gas it does not so readily recon-
dense into its liquid form, and it is, therefore, more easy to
deal with, than a mere vapour produced by mechanical
means.

However, in producing a gas from oil by means of a
heat treatment, there is always the likelihood of forming
carbon deposits in the vaporising chamber, particularly if
the temperature is so high that the fuel cracks. We have
previously seen that under certain circumstances trouble is
likely to occur through the recondensation of vaporised
liquid, and this trouble is cumulative, for if a missfire occurs
through the condensation of a portion of an incoming
charge, that part of the fuel which has entered the engine
cylinder is likely to further condense and to spoil the
following charge.

The presence of too much hydrocarbon, or too little
when the mixture consists of paraffin vapour, is very much
more important than when petrol vapour is employed ; and
whereas in the latter case ignition can take place between
the limits of 1.2 per cent, of petrol vapour to air and 5.5
per cent, at ordinary temperature pressure, or between
1.84 and 0.4 times the correct amount of air, yet in the
case of paraffin only about one half this latitude is
possible.

For this reason it is imperative, when using paraffin.

DIFFICULTY IN USING PARAFFIN 1 35

that the proportions of fuel and air should be exactly
measured.

Now, as the volume of vapour produced from a liquid is
enormously greater than the volume of the liquid itself
{i.e.^ in the case of petrol it is 190 to 230 times as great),
it is much easier to measure a volume of vapour than a
volume of liquid. Furthermore, owing to the very small
volumes of liquid which pass to the ordinary automobile
engine, it is extremely difficult to measure these volumes
with any great degree of accuracy. The author, therefore,
contends that the most practical method of dealing with
the question of paraffin carburation is first to convert
the fuel into a fixed gas, using some form of measuring
device which fairly proportions the amount of liquid fuel
to the air passing to the engine, and to measure exactly
and proportion the amount of fuel vapour to the total
amount of air.

We have, in the internal combustion engine, at our
disposal a certain amount of waste heat in the exhaust
of the order of 40 per cent, of the total heat of the fuel,
and by utilising the heat in a proper manner we can,
without much cost, fix up an oil gas producer.

There has been in the past a great divergence of
opinion as to what is the proper method of utilising heat
in order to obtain satisfactory carburation, and at the
present time, for automobile work, there only appears to be
one system which really works well. This system consists
in an arrangement of evaporating paraffin in the presence
of a small quantity of air, and then either using the mixture
at its original temperature, or still further raising its tempera-
ture and mixing it with such an amount of additional air as
will produce an explosive mixture. A definite figure for
the necessary quantity of air which should be mixed with
the fuel during its first heating process is between 10 and
20 per cent, of the total air required. The evaporated
fuel should be superheated before mixing with the main
air supplied, with the following objects — {a) of producing

136

CARBURATION

a fog of extremely fine texture, and {b) of producing a
fixed gas. With regard to the necessity of the former,
it only needs reference to a previous chapter, in which
the author shows how the surface of liquid exposed to
the air supplied is in proportion to the cube root of the
decrease of the diameter of the individual particles or
globules of liquid, and the second consideration, viz., that
of producing a fixed gas, is very obvious when one con-
siders the arguments in connection with the formation of
the inlet pipe. Although this operation may be complete
in the vaporiser, yet on mixing such a charge with extra
air, when the gas is properly fixed, any paraffin condensed
in this form has practically no wetting property, and
differs from the coarser particles formed by spraying the
fuel. The coarser particles may burn satisfactorily in a
comparatively slow speed stationary engine, but when we
come into high speed automobile work the time element
is so short that it is absolutely essential that the particles
of hydrocarbon should be as finely divided as possible,
in order that the rate of propagation of the flame through
the mixture shall be as rapid and complete as possible.

It is obviously important that the fuel particles should
be broken up into their smallest possible dimensions, and
that sufficient heat be added, so that when the additional
air is mixed with the finely divided particles of fuel there
should be no recondensation in the mixing valve or the
inlet pipe.

The most interesting and practical system of which
the author is aware at the present time is that devised
by the G.C. Vaporiser, Ltd., and the author has recently
carried out some trials with an apparatus of this type in
which the results were most satisfactory.

It is necessary first to consider the question of
temperature. Evaporation cannot be complete unless
the temperature to which the fuel particles is exposed
is at least 300" C, as the maximum boiling point of
the heaviest fraction is 300° C. It is obviousl}- impos-

THE G.C. VAPORISER 1 37

sible to obtain complete evaporation unless this tempera
ture is reached. In the G.C. arrangement a temperature
of 300 C. or thereabout is aimed at, and in order
that this temperature should be maintained throughout
all conditions of working, the G.C. apparatus comprises
a thermal storage of considerable capacity. J The capacity
of this thermal storage depends on the duties for which
the apparatus is required. For instance, if a car is to
be fitted for use in traffic or any considerable periods
of light running, it is necessary to have a sufficient
thermal storage capacity in order that the apparatus
should not cool down too much in working. The
thermal storage is obtained by means of the exhaust
silencer, through which the gas is passed in a circuitous
path, and the storage of heat is taken up by particles of
metal having a considerable capacity for the storage of
heat. The passages for the hot gas through this thermal
storage apparatus are arranged in a similar manner to
those which one generally finds in a Lancashire boiler,
viz., the exhaust gas is passed through from one end to
the other and returned outside the original flue, an
annular space being interposed between the two passages
for the vaporisation of the paraffin. By this arrangement;
although at the entering end the greatest temperature is
reached, at the remote end the temperature of the whole
apparatus is about a mean of the maximum and minimum
temperature of the exhaust. By the time the gases have
returned along the outer casing their temperature is still
further reduced, so that at the entering end, in addition
to having the maximum temperature at the centre, we
have the minimum temperature outside. One might
consider that, to be on the safe side, it would be necessary
to have the temperature somewhat higher than the
maximum temperature of boiling of the heaviest particles
in the fuel, but then difficulties occur due to a certain
amount of slow combustion going on in the fuel itself
when oxygen is allowed to reach it. The amount of

138

CARBURATION

this combustion has not been definitely determined, but
Professor Morgan's investigations show how, as the gas
and air pass through a heated tube, the proportions of
CO at various points in the tube vary, thus showing that
combustion is taking place in a manner which has been
described by Dr Bone in connection with the surface
combustion of gases.

Professor Morgan heated his mixture to a temperature
of 600° C. for his second series of experiments, and this
temperature was found to be a critical temperature at
which combustion took place in mixtures of paraffin vapour
and air. It is therefore obvious that in any system of
vaporising of paraffin, in order to avoid the combination
of the carbon in the fuel with the oxygen in the air, a
temperature of less than 600"^ C. must be worked at.
Professor Morgan states that below this temperature these
reactions are so slow as to be inappreciable under the
conditions prevailing in the petrol engine, but above this
temperature the reactions are rapid, giving rise to in-
flammation or a condition approaching thereto. He
further points out that the ratio of air to fuel had no
effect on this critical temperature. It would be difficult to
state at this stage of our knowledge whether the speed of
the passage of the gas through the heated tubes had much
effect upon the result, and in Professor Morgan's test the
speed of the gas was slow, and this, of course, is the case in
the G.C. apparatus.

Reverting now to the G.C. vaporiser system, one point
in particular is most interesting, and that is, that as the hot
gas is led away from the vaporiser to the mixing valve no
precipitation of liquid is apparent, and even though in the
mixing valve the majority of the air is added to the
vaporised fuel, and the temperature is reduced to practically
that of the atmosphere, yet there is no apparent precipita-
tion of liquid here. This is most important, as obviously
the low temperature of the vapour entering the engine
enables a greater weight of explosive mixture to be intro-

ACTION IN A VAPORISER

139

duced to the engine cylinders in unit time than is possible
in any other system of paraffin vaporisation, where the
explosive mixture is led to the engine at a very high
temperature. This low temperature of the carburetted air
is only possible on account of the more or less fixed nature
of the vapour before it is admixed with the air in order to
form a combustible mixture.

Table LIT. — Consumption pkr Horse-Power Hour

Average Load.

I. Petrol Engine. 2. Diesel £ngmc.

Pint.

Pence per
Pint.

Pence per
H.P.

0.52
O.IO

Pint.

Pence per
Pint.

Pence per
H.P.

Fuel -
Oil -

0.70
0.02

0-75
5.00

0.60

i 0.03

0.30
5.00

0.18
0.15

Fuel and lubricant per 1 1. P., o.62d. Per H.P., 0.33d.

3. G.C. System.

Pint.

0.65
0.018

Pence per
Pint.

Pence per
H.P.

Fuel -
Oil -

0-37
5.00

0.24
0.09

Fuel and lubricant per H.P., 0.33d, j

The Maintenance Expenses (15 per cent.), Depreciation
(15 per cent.), Interest on Capital (5 per cent.) per
Horse-Power Hour.

Number of Daily Service Hours.

I and 3. Explosion engine
2. Diesel engine

0.15
0-43

O.IO

0.29

0.07 pence per H.P.

0.22 ,, ,,

140

CARBURATION

The previous arguments are not given in any way as
adversely criticising the Diesel engine, either in principle
or as a commercial proposition, but to stimulate others
who are working on the problem of paraffin or oil as a fuel
for internal combustion engines, and to show them that it
is quite possible to obtain very satisfactory commercial
results with other methods than those adopted for the
Diesel engine. That there is an undoubted field for the
use of paraffin for the internal combustion engine is un-
disputed, but at the same time one must carefully bear in
mind there are particular cases to which the use of paraffin .,
is applicable. ^^■1

Other really successful paraffin systems include the
Morris, in which a modulating pin device is employed for
regulating the fuel supply, a small percentage of air is
allowed to pass with the fuel through a vaporising tube
and the remainder of the air is added at the mixing value, n
No thermal storage is provided, ^||

The Standard has also undergone satisfactory trials and
operates in a somewhat similar manner to the G.C.

CHAPTER XII

EXHAUST GAS ANALYSES

In 1907 Dr Dugald Clerk, who is probably the greatest
authority on- the internal combustion engine, read an
important paper before the Institution of Automobile
Engineers on the principles of carburetting as determined
by exhaust gas analyses. He was thus the first to draw
public attention to the importance of this subject of
determining what was taking place in the cylinders of
an internal combustion engine. Attention had already
been drawn to the question of the importance of making
an examination of the exhaust gases, at the time of the
trials made by the Royal x^utomobile Club, in connection
with carburation in the motor car engine of the time.
Sufficient indication was not, however, previously given
that examination of the exhaust gases was to be the
determining factor in awarding marks in connection with
these trials.

Entrants for the trials were under the impression that
the emission of smoke only was to be adjudicated upon, and
there was somewhat of a revelation when the Committee's
report was published, as it was shown that an amount of
carbonic oxide equal to at least 2 per cent., and generally
more, was prevalent in the exhaust gases of the majority
of the cars under consideration, and that this percentage
showed how imperfect was the carburation at that time.

The modern conditions of high speed motors make it
extremely difficult to design a carburettor which will
function correctly throughout the prevailing ranges of load
and speed, and it is by means of the analyses of the

141

CARBURATION

exhaust gases that we are most easily able to determine
what is taking place under various working conditions. J

It must not be considered that by exhaust gas analysis
alone can the true determination be made, and it is
extremely difficult to obtain, in the first place, fair average
samples of exhaust gases, on account of the possibilities of
missfiring, when charges are liable to escape into the exhaust
in an unburnt state, and thus mingle with the sample of
gases to be analysed. Furthermore, there is the possibility
of air leaking into the samples unless the sampling is very
carefully carried out. This leakage of air is, in some
instances, due to pulsations in the exhaust pipe causing
a certain amount of back flow of air up the pipe, after a
partial vacuum has been produced immediately after the
ejection of a burnt charge. This mingling, of what one
might term foreign substances, gives a false impression as
to what is actually taking place in the engine cylinders, so
that considerable caution must be exercised in comparing
the analyses taken from the exhaust of various engines
unless very great care is taken in the sampling process.

A common method of determining the degree of success
of the regulation of a carburettor is to examine the flame
coming from the exhaust valve port under the various
changes of conditions, and a carburettor can be regulated
to a certain extent by noting that the flame leaving the
exhaust port is not a long, luminous one, but short, blue,
and non-luminous. This blue flame is supposed to indicate
fairly complete combustion within the cylinder ; but the
method of testing is very crude, and gives but little real
knowledge of what the carburettor is doing throughout the
whole range.

Referring now to the trials of the Royal Automobile
Club, Dr Dugald Clerk points out that whilst four of the
cars under examination discharged an exhaust containing
under two per cent, of carbonic oxide, eight cars dis-
charged more than this quantity. The samples were taken
by discharging the exhaust into copper drums, each about

METHOD OF INVESTIGATION I43

800 cub. in. capacity, two samples being taken from
each car.

A method of making a complete investigation is as
follows. Exhaust samples could be taken —

(a) When the car was standing on the level with the

engine running as slowly as possible.
{b) With the car still standing, but the engine running

at various rates of speed from 600 up to 1,000

revs, per min.
{c) With the car running on the level at about 18 to
' 20 miles an hour with the throttle only partially

opened.
{d) With the car climbing a hill, the engine running

so that it gives approximately its maximum

output.

Let us first consider the method of taking the samples,
and it will be evident from the foregoing remarks that it
is most satisfactory to take off a sampling connection as
near as possible to the exhaust valves, so that the effect of
pulsations does not appear in the sampling apparatus.
Furthermore, the samples should be taken over a consider-
able period, so that a fair average sample of what is
occurring is collected in the sampling vessel. When the
sample has been collected it can be examined by Mr
Horatio Ballantyne's method, which is as follows : —

CO, CO2, and O.^ are first determined by the usual
gas volumetric method, a known volume of the gas, about
50 c.c, is treated in succession with (i) caustic potash
solution (50 grms. KOH plus 100 grms, of water); (2)
alkaline pyrogallol solution (5 grms. pyrogallol, 50 grms.
KOH, and 100 c.c. of water) ; and (3) acid cuprous
chloride solution (used and fresh respectively), followed
by caustic potash solution. The proportions of COg, O2,
and CO respectively are thus ascertained. The total time
taken to make a rough analysis of exhaust gas by this
method is about 10 to 15 minutes, and the various gases

144

CAKBURATION

are absorbed by the various solutions, and the reduction
in volume of the samples is read off.

The proportions of the various gases are usually given
in percentages by volume to the total.

Ethylene, hydrogen, methane, and nitrogen remain to
be determined, and the usual gas volumetric methods may
be employed. In making a rough analysis, however, these
are frequently all lumped together and put down as
nitrogen, etc. Mr Ballantyne states that he has found
that for nearly all practical purposes it is unnecessary to
determine these constituents by direct analysis, and an
important saving in time and trouble is thus effected. The
results are arrived at as follows : —

The proportions of hydrogen and methane bear a
definite relation to the proportion of CO, namely, the
percentage of CO X 0.36 = the percentage of H, and the
percentage of CO x 0.12 = the percentage of CH^. These
two gases are, therefore, determined by simple multiplica-
tion. The nitrogen is determined by the difference, as in
ordinary analyses.

The following table shows an approximate analysis of
three samples of exhaust gas : —

Table LIII.

By analysis - ^
By calculation -

CO
CO.,

0.."

CHj

No ■

1.8

5-6

10.6

0.6

0.2

81.2

2.4

r 1.0

2.2

0.8

0-3
^3-3

2.2

1 1.8

0.6

0.8

0-3
84-3

100. 0

lOO.O

100.0

The calculated results obtained, as above described, may
be regarded as correct within the limits of error of an
analysis by gas volumetric methods.

COMPLETENESS OF COMBUSTION I45

Professor B. Hopkinson, of Cambridge University,
about the year 1907, made a large number of experiments
upon exhaust* gas analyses, and his results were embodied
in a paper read before the British Association in 1907.
These experiments were made on a four-cylinder Daimler
engine, with cylinders 3.56 in. diameter by 5.11 in. stroke,
and the engine was run under full load at a constant speed
of 750 revs, per min. The Hopkinson tests are particularly
interesting in this respect — they show that the percentage
of CO2 mounts from 10.9 to 13.5 per cent, by volume, as
the horse-power of the engine increases to its maximum,
and at the same time the thermal efficiency of the engine
increases up to that point. Above that point and onwards,
as the percentage of COg falls from 13.5 to 9.6, the brake
load curve is practically flat, and is at its peak. During
this period it is interesting to note that the percentage of
O., varied from 0.2 to zero, and the percentage of CO,
which was previously a zero quantity, increased from 0.7
to 6.25.

As the percentage of CO was allowed to increase up to
1 1.6, the brake load rapidly fell off. The whole of this
time the thermal efficiency of the engine was dropping
rapidly.

It will thus be seen that within considerably wide
limits a rich mixture of fuel maintains the maximum
horse-power at a practically constant value, whilst the
thermal efficiency drops off as the mixture is enriched, and
that the most economical point to run is when the CO., is \j
13.5 per cent, by volume, the O.2 is 0.2 per cent., and the
CO is 0.7 per cent., dropping down to zero. At this time
the thermal efficiency of the Daimler engine under con-
sideration was 0.26, or 26 per cent.

Power is in some cases more important than thermal
efficiency, and this can be obtained in many instances
by using a rich mixture which is not completely
consumed.

146

CARBURATION

Table LIV. — Experiments of Prof. Bertram Hopkinson
AND Mr L. G. Morse on a Daimler Engine.

Petrol Consumption
in lbs. per 1,000 revs.

Thermal efficiency
CO., measured

O2 " „
CO „

Ho „
No by difference -
Total Oo calcu-
lated from No -
HoO calculated -

0.I8I.

0.191.

0.197.

0.217.

0.250.

0.292.

0.244

0.252

0.261

0.238

0.204

0.162

10.9

T2.8

13-5

10.6

9.6

3.6

1-5

0.2

0.7

6.25

II. 6

2.1

2.65

8.7

22.4

21.5

21.3

19.4

,5.8

16.2

16.8

17.2

15-2

Professor Hopkinson's experiments are particularly
valuable, showing that an engine adjusted for maximum
thermal efficiency at full power discharges an exhaust
which is free from any objection, but an engine so
adjusted may also have an innocuous exhaust at lighter
loads, but this by no means follows ; it depends upon the
nature and design of the carburettor. If, however, the
carburettor is designed to function by some automatic air
valve device, it does not always follow that this functioning
will take place at the correct moment, and there may
be positions in the carburettor curve where large per-
centages of carbonic oxide are discharged. It may occur,
for example, that the speed of an engine may be kept
perfectly constant, but the position of throttle opening,
and consequently the carburated mixture passing through
the carburettor in any unit time, may vary through wide
limits owing to the variations of road resistance, and it
is, therefore, obvious that neither engine speed alone nor
throttle opening alone can in any way accurately govern
the amount of fuel and air passing to the engine.

Now it is useful for us to make a comparison between
the figures as given above with those obtained by Dr

EFFECT OF MIXTURE STRENGTH 1 47

Watson, and given in his paper on thermal and combustion
efficiency, and we find that the most efficient all-round
mixture was obtained by Dr Watson when the ratio of air
to fuel by weight was from 15 or 16 to i. At this time
the thermal efficiency was 0.249, or practically 25 per cent.,
and the mean effective pressure in the cylinder varied from
81 lbs. per sq. in. to 84 lbs. per sq. in. gauge.

When the strength of the mixture was weakened, and
the ratio of air to fuel by weight was increased to 18.7 to
I, the thermal efficiency dropped to 0.230, and the mean
effective pressure to 65.4 lbs. per sq. in. As the mixture
was still further weakened, and the ratio of air to fuel was
19.4 to I, the mean effective pressure dropped further to
55.4 lbs. per sq. in., and the thermal efficiency to 0.196.

At the other end of the scale, however, when the
mixture was strengthened, we find in Dr Watson's tests
that, as the ratio of air to fuel was increased to 12.3 to i,
the mean effective pressure increased slightly to 85.7 lbs.
per sq. in., with a dropping thermal efficiency to 0.208. As
the mixture strength was still further increased to 11.7 to
I, the mean effective pressure dropped slightly to 83.6 lbs.
per sq. in., and the thermal efficiency dropped to 0.173.

Naturally the exact points where these pressures rise
and fall depends not only on the mixture's strength, but to
a certain extent upon the engine compression, and also
upon the design of the engine itself The figures that
are given are merely indications of what actually occurs
in practice.

Dr Watson's deductions were to the effect that when
free oxygen appeared in the exhaust there was no carbonic
oxide, and with a weak mixture one naturally finds an
excess of free oxygen, and rarely finds carbonic oxide.

Conclusions which can be drawn from an examination
of exhaust gas analyses as to conditions of perfect com-
bustion may be cited as follows : —

The most important point is that completed combustion
by no means follows because there is an excess of oxygen.

148

CARBURATION

For instance, a carburettor may be adjusted in such a way
as to give a substantial excess of oxygen throughout its
whole range, and yet carbonic oxide is not necessarily
suppressed, nor is complete combustion obtained. One can
see, from an examination of various tables of exhaust gases,
that it does not follow by any means that the percentage of
carbonic oxide bears any definite relation to the percfentage
of free oxygen, and in working out an exhaust gas analysis
for the comparison of the merits of different engines or
different adjustments, the total fuel consumed should be
tested in any given experiment, and from the exhaust gas
analysis there should be calculated the proportion of that
fuel which is rejected without burning.

An estimate can be made from the exhaust gas
analysis as to the amount of air taken into the engine.
For example, if we know the quantity of fuel supplied
per minute and the percentage of free oxygen in the
exhaust, we can calculate the proportion that this free
oxygen bears to the total amount required theoretically
for complete combustion. If, for example, the free oxygen
should be 1.35 per cent., this is equivalent to 6 per cent,
of the total oxygen taken by the engine. Making allow-
ances of two-thirds of this to consume unburnt hydrogen
and carbon in the exhaust, the remainder, or 2 per cent,
shows the excess of air theoretically required to burn
the fuel. The amount of vapour given per gallon of fuel
will be 24.7 cub. ft. per gallon in the case of heptane,
and 22.6 cub. ft. per gallon with octane, and 20.8 for
nonane.

The following interesting table is taken from the
R.A.C. Report, on the Limit carburettor, fitted to a four-
cylinder 80 mm. X 120 mm. engine, and is useful as showing
the possibilities of an instrument of this type : —

TEST FIGURES

149

»o

0 "

n On :

so n 00 N

Tl-OO

-1-

ro 0' •

N N d d

d CO
00

vO On

UT) 00 :

rO 0 t^ N

.-^s 00

C CO

10 0

-4

ro rJ d d

»o

VO VO

r->.

VO r^ :

Tl-

LO Tt N tJ-

e^ ro

i "^

i^ 6 •

rj CO M d

d ^i

1— 1

l-H

ro lo

- 1

so 6 -^i

00 rt w .-t:
po w d ^

VO hH

d to

<+j

t^ Qs

LT)

On vo r^

00 Tt hH .-;:

0 t-*

•^
^

ON d ij^

•

fo d d ^

-' 4
00

ro N

':!-

0
0

00 VO ON

vd d -^

ro ^66

NO PO

d 4

t^ '^

Tt ON :
00 d *

0\ M rl- HH

«r> M d d

ri- 0

d 4

'i- ON

I—

0 ^ M

M Tt- >0 M

Tt- ro

4 6 ^

•

ro '^ 6 6

d 4

a»

C) 10

n «o t-H

;

uo 0 r-~ w

q vq

li-)

d d M

•

N N d d

- PO

„,--— "v

' ^ 'I

il '^

' oT ' ti '

1 1

3"x
i- 0

r; OJ

, 0 , t- :;

^ ^

e per minute
see descript;

Its per
above (m

below(st
arbon di

bon mon

rogen, pe
thane.

^ Si,

bJD 0

C/2

0 C

c ^-^

3 (D -^ -"

c/T .X"

evolutions of engi
rake horse-power

c t^ y £ c

C/1

W3 •,«

trial)

uel consumptio
power hour

ariation of mi
expressed as pe
age variation fro
mean mixture i

nine tests
xhaust gas anal

per cent.-
xhaust gas analy

per cent. -
xhaust gas analy;

:; ::

P^pq

W W

oa
OS

W
O

PART II

CHAPTER XIII

CARBURETTORS

The " Bailey-Dale " Carburettor. — This carburettor is
somewhat unique, being of the single lever control
mechanically automatic type. Two adjustable jets with
their respective choke tubes are features of this design,
and are arranged in such a manner that they are visible
and adjustable whilst the carburettor is working.

It \v\\\ be noted that a shutter is provided to give access
to these jets and choke tubes, and they are therefore readily
accessible.

The smaller or pilot combination of jet and choke tube
is of such dimensions that at the lowest engine speed the
velocity of air passing the jet is sufficiently high to ensure
easy starting and the proper atomisation of the petrol, and
this can only be accomplished by means of a reasonably
high depression. The designer of this instrument considers
that a depression of about 14 in. is the most suitable for
this purpose. This jet is first brought into operation when
the throttle is opened.

The main jet and choke tube combination, which are
naturally of larger dimensions, are automatically brought
into action by a further movement of the throttle, in
accordance with the requirements of the engine.

In order to make the necessary corrections for high
engine speed in this instance, arrangements are made in

151

152

CARBURATION

BAILEV-DALE CARBURETTOR 1 53

the form of an automatic air device working in conjunction
with the throttle. The air shutter provided for this
purpose can be adjusted to come into action at any point
in the travel of the throttle, thus enabling any desired
petrol or air curve to be obtained to suit any particular
engine.

One of the features of this instrument is the split
barrel throttle, which remains tight at all times, and
therefore does not leak if any wear comes upon it. It will
also be noticed that this throttle is of the type which closes
on two sides, viz., the inlet and the outlet, and the throttle
spindle is of large diameter made of steel working in a
long bush so as to minimise wear and tear.

This carburettor is of the variable suction type, and the
adjustments can be carried out as follows : firstly, adjust-
ment of the pilot jet ; secondly, that of the main jet ; and
thirdly, that of the auxiliary air supply.

The makers advise that the diameter of the main choke
should be a fifth to a quarter of the diameter of one of the
engine cylinders, and that in conjunction with the largest
main choke tube the largest auxiliary choke tube should
be also employed.

An adjusting screw is fitted in the pilot jet, and this
should be so arranged at starting that an ample supply of
fuel is passed, and when the engine is running with the
throttle in such a position that the pilot jet only is in use,
the screw controlling the flow of fuel through this jet can
easily be regulated. Care should be taken that the auto-
matic air shutter does not come into operation before the
main jet comes into action, and as the adjusting screw of
the pilot jet is gradually closed down the speed of the
engine will increase until such a point as the most
economical and efficient mixture is arrived at. On further
screwing down the jet orifice, the engine speed will again
fall off due to a weak mixture, and the mixture must not
be weakened beyond this point.

The main jet can now be regulated by means of the

154

CARBURATION

adjusting screw until maximum power is obtained with
about half throttle opening, and finally the auxiliary air
supply can be adjusted when the car is taken to a
suitable hill.

Binks. — The Binks carburettor is of the two-jet type,
and of its principal claims the first is that in place of an
ordinary rotating or butterfly throttle, valves of the mush-
room type are fitted one above the other on a vertical
spindle. In one type of Binks carburettor the spindle is
horizontal, but the principle is practically the same. In the
first place, valves of the mushroom type are easier to keep
tight on their seats, and the designer of the carburettor
places great importance on the tightness of the valves.
The two jets consist of a small one for slow running, with
a separate choke tube and a main jet for ordinary working
mixtures. By means of the small jet it is stated that all
speeds up to about 1 5 m.p.h. can be obtained, and as the
two throttles work conjointly, that which controls the small
jet and choke tube naturally moves slightly in advance of
the main throttle. These valves are so arranged that the
suction of the engine tends to keep them closed, and a
spring is provided to hold the main valve on its seat.
This type of carburettor is one which la)'s itself open to
a very large variation in adjustment, and as six choke
tubes are provided with each carburettor, combinations
with the various jets give a very wide range. Further-
more, great facilities are provided for making the necessary
alterations, as it is claimed by the designer that an im-
portant point in carburettor construction should be facility
for making adjustments as necessity arises.

A useful feature is embodied in the design of this
carburettor, whereby a single operation of the lever brings
first one and then the other jet into use, whilst a still further
movement of the lever permits an extra supply of air to
be drawn into the induction pipe. By means of this
arrangement it is possible to ascertain, when running.

filNKS CARBURETTOR

155

whether the air supply is sufficient or not at high speed,
and if it is found that the mixture is too rich under

these conditions, the pick-up will be increased as the extra
air is admitted, thus showing that the main jet is too

156

CARBUKATION

large. In the design of this carburettor great importance
is attached to a high velocity past the jet, and it is
claimed that perfect carburation can only be obtained by
the mechanical action due to a high air velocity. By
means of the use of a truly shaped Venturi tube it is
naturally possible to pass a very much larger quantity of
air through a given aperture than would be the case were
the choke tube improperly designed. It is claim.ed, there-
fore, that in the design of this carburettor a maximum
amount of air for a given size choke tube is drawn into
the engine. The heating of this carburettor by hot air
eliminates a water jacket, with its attendant pipes and con-
nections. It naturally does not signify as to how the heat
is applied, as long as there is sufficient to supply the latent
heat of evaporation of the fuel.

The Brewer Carburettor. — The principal features
embodied in the design of this instrument are a variably
progressive lift of the fuel needle in comparison to the
lift of the air valve, a jet orifice whose coefficient of dis-
charge under all ordinary conditions is approximately
constant, and a fine atomising of the fuel near the orifice.

The construction of the carburettor is such that it
works under a variable depression, as the author has found
from experiment that the ordinary constant suction instru-
ment has limitations except perhaps in very few instances.
At any rate he is of firm opinion that when a so-called
constant suction carburettor is called upon to perform
high duties, it no longer remains working under its normal
or designed depression.

Further, a higher depression than is usually suitable
for a constant suction design, is often desirable, in order
to effect atomisation of the fuel when the discharge rate
is high, and the Brewer carburettor is designed to work
at a depression as high as 25 in. of water at its maximum
limit. Further its lower limit of working before the air
valve lifts is 7 to 8 in. of water, and by keeping this

BREWER CARBURETTOR I 57

pressure low, the weight of the moving part and hence
its inertia can be kept down.

Under slow running light conditions the depression
in the mixing chamber is 4 in. of water, but owing to
the great restriction caused by the Venturi tube round the
jet orifice the air velocity at this point is high.

Observations made with water show that when an air
stream is blown through the Venturi tube at ordinary
working pressure, the water issues from the nozzle in such
a fine spray that it can scarcely be seen.

The object of the progressive movement of the fuel
needle scarcely requires enlarging upon, as the necessity
of allowing a larger orifice for cold fuel than for warm
fuel has already been explained in another part of this
book. Also it has been shown that when the engine and
carburettor are cold at starting, a larger proportion of
fuel is required on account of imperfect vaporisation of the
whole of the fractions.

The design of the carburettor can be grasped by refer-
ence to the accompanying sections (Fig. 29). F is the
main carburettor casting enclosed at the top by the dis-
mantling cap c, and having attached at the bottom the
bowl of the float chamber M. N is the concentric float.
Set in a socket formed in the body of the carburettor is
the main air valve j, capable of being reciprocated verti-
cally by the suction of the engine. The ridge or cam-
shaped projection Q at the top of this throttle valve bears
against the hooked end of the lever G pivoted at E. This
lever in its turn bears against the flange formed on the jet
needle carrier D, which is seen to be surrounded by a
spring set between the flange already mentioned and the
underface of the dismantling cap C. Within this carrier D
is the vertical jet needle B, with grooves of gradually in-
creasing depth formed in its lower end. It is cross-cut at
the top for adjustment in the jet needle carrier, by means
of the screwed end. Within the lower part of the air valve
J is the Venturi choke tube L secured to it. The grooved

158

:arburation

end of the vertical jet needle passes into the vertical fuel
nozzle O, which is screwed into the lower portion of the
body F of the carburettor.

The principal feature is the control of the fuel valve B
by means of the air valve j. Contrary to the common
practice, in which the air and fuel valves are directly con-
nected, in this case the two valves B and J are so connected
that their relative openings are capable of being varied,
the movement of the air valve j transmitting movement to
the fuel valve B through the medium of the hinged finger
or claw G. The latter operates as a lever, the fulcrum or
fixed pivot E of this lever being attached to some con-
venient part of the carburettor body, and the toe of the
lever pressing against the carrier D, which, as mentioned,
holds the fuel needle B for regulating the flow of the fuel
through the nozzle or jet O.

Movement is imparted to the needle carrier D by the
air valve J through the medium of this lever, and for this
purpose the air valve has formed upon it a ridge, or cam-
shaped projection Q, already mentioned, which is so
located upon the air valve J that a rotation of the latter
brings the point of contact of the ridge, or cam-shaped
piece, into different positions upon the heel of the inter-
mediate lever G, thus changing the extent of its leverage.

The original setting of the fuel valve B with regard to
its orifice will not be altered at the zero, or slow running
position, by a rotation of the actuating air valve, but the
differential movement through the medium of the heel of
the lever G increases from zero to a maximum as the air
valve throttle rises from its seat.

When setting the fuel feed and air supply proportions
any rotation of the air valve will give a progressive increase,
or decrease, of lift to the fuel valve. The setting remains
constant until again adjusted, the air valve J being
prevented from rotating by notches in the cam-shaped
piece Q into which the lever G drops. Co-operating with
the vertical fuel nozzle O is a tubular extension of the air

BREWER CARBURETTOR

159

Fi(^.. 29.— The Vertical Sections of the Brewer Carburettor (diagrammatic).

A. Dust cap.

B. Vertical jet needle with grooves of

gradually increasing depth.

C. Dismantling cap.

D. Jet needle-carrier in which needle

can be adjusted vertically.

E. Fulcrum spindle of lever G.

F. Main carburettor casting.

G. Lever which receives motion from

air valve J, and imparts motion
to carrier D, and jet needle B.

J. Air valve.

L. Venturi choke tube secured in the
stem of air valve J.

M. Bowl of float chamber,

N. Cork or metal float.

O. Vertical fuel nozzle secured in base

of body F.
P. Nut securing float chamber bowl.
Q. Cam - shaped projection on air

valve J.
R. Float chamber needle valve.
T. Float lever.
U. Petrol feed.
X. Main air inlet.
Y. Induction pipe connection.

i6o

CARBURATION

valve J provided with a conical sleeve or choke tube L,
which rises and falls around the outside of the fuel nozzle,
according to the rise and fall of the air valve J, leaving
an annular opening through which the primary air passes
from the air supply and mixes with and atomises the fuel
coming from the inside of the nozzle along the grooves of
the valve spindle.

When running dead slow, this sleeve L admits the
whole of the mixture which passes to the induction pipe,
but as the air valve J is raised, it opens up not only the
main air supply X, due to the air valve leaving its seating
proper, but also admits an increased initial
supply due to the rising of the conical choke
tube L. The raising of the air valve J also
raises the fuel valve B and admits more fuel,
as before mentioned.

An advantage of the design is that the
complete carburettor can be manufactured with
very little machining, since its operation is in-
dependent of accurate fitting of the parts con-
trolling the air supply.

Figs. 1 1 and 30 are enlarged views of the
vertical jet and needle which are used in this
carburettor. The jet tube is of larger diameter
than usual, 4 mm. bore being a standard size.
Into this jet, as shown, there passes a long fluted needle
which projects i in. in the closed position, the total maximum
lift being f in. to h in. Although the fluted needle in itself
is not new, the shape of the flutes is very important, as it
gives a practically constant coefficient of discharge of the
orifice at all working positions of the needle under fuel
heads of from 10 in. to 25 in. of water pressure.

The coefficient of discharge of an orifice is a factor
which depends, firstly, upon the flow of fuel per unit area,
and, secondly, upon the square root of the pressure
difference between the atmospheric pressure in the mixing
chamber in the vicinity of the jet.

Vu.. 30.

6rew£R carburettor i6i

Now, if the depression or suction is constant, the
coefficient of discharge of the orifice is a certain constant
depending upon the amount of the suction, whatever may
be the area of the orifice or the amount of fuel flowing.
'^However, if the suction varies, the constant is different for
each value of the suction ; for instance, at a lO-in. suction
the constant is 0.568, and that figure multiplied by the
flow of fuel in gallons per hour per square mm. of orifice
will give the coefficient of discharge of the orifice.

When the suction increases to 15 in. of water-head the
constant becomes 0.453, ^^^ ^^ 20 in. it is 0.400, and so
on. This variation of figure, as before mentioned, is
governed by the square root of the pressure difference
in the same way that the flow of the air through the
carburettor is governed. If, therefore, a constant mixture
is to be produced the flow of fuel per unit area through
the orifice, under increasing pressures, must increase
approximately as the square root of the pressure difference,
i.e., at the same rate as the flow of the air increases.

Tests made with a liquid flowing through this type of
orifice show that with the constant coefficient of fuel dis-
charge which is very nearly obtained, the proportions of
the mixture will remain the same under all ordinary work-
ing conditions, owing to the actual flow of fuel increasing
at the same rate as the flow of air.

The flutes are of segmental section with rounded
corners, increasing in depth and width from their zero
position to the point of the needle, and the coefficient of
discharge of such an orifice is of the order of 0.440, that of
a round hole being of the order of 0.770, when the length
of the orifice is four or five times its diameter. The object
also of such an orifice as this is to give high jet friction
with a good spraying effect, and, by means of shaping the
outside of the jet tube as shov/n, and fitting a small choke
tube which lifts with the air valve, concentration of
primary air flow round the fuel orifice is obtained.

The object of the proportionate adjustment is to de-
1 1

l62

CARBURATION

crease the opening of the fuel orifice when the instrument
and the fuel become warmed up, as the flow of fuel through
an orifice becomes from lO per cent, to 15 per cent, more
rapid at the upper limit of temperature reached in ordinary
motor car work.

Another type of this device has been designed for pro-
duction in die casting, and although the principle is the
same, some modification in detail has been embodied,
firstly, in order to enable an extra hot air supply to be
admitted around the jet, which, by the way, can be alter-
natively replaced by paraffin vapour, and this transforms
the instrument into a paraffin carburettor. Secondly, the
instrument has been fitted with a butterfly throttle of the
conventional type in order to bring it more into popular
line, and, further, one type can be made universal for any
arrangement of fuel or air openings to suit individual
engines.

The differential movement in the latest model of the
Brewer carburettor is so designed that a single direct
movement of one control both increases the proportion
of fuel progressively at all speeds of the engine, and at
the same time gives a larger fuel opening at zero position
of the needle, for slow running.

The larger model Brewer carburettor is modified in
order to simplify the control gear and to provide a straight
line movement for adjustment of the regulating device.
In order to obtain this, the fulcrum of the actuating lever
X is placed upon the air valve itself and the adjustable lift
is given by moving a contact piece forward or backward
along the free end of this lever. This can be done by
means of a Bowden wire control, and the device which
holds the end of this control in position is capable of
movement in a slot, fully covered by its locking device, so
that the slow running position of the needle can be located
by fixing the control in such a position that the forked
end of the lever is suitably displaced so as to raise or
lower the needle permanently in the jet.

BREWER AUTOMATIC CARBURETTOR

163

It will be seen that the differential movement is then
provided by sliding the contact piece V forward or back-

ward along the lever O.

ctS

An alternative method is to make (the axis of move-
ment of the piece v oblique to the face of the lever O upon
which it works. The object of this is to alter the zero or
slow running position simultaneously with einy alteration
for proportions of mixture. Thus, if it is desired to

164

CARBURATION

weaken the mixture by giving the fuel needle a smaller
travel, the needle at zero position will be allowed to enter
further into the jet orifice, and thus weaken the mixture
at slow running. A design has been prepared by the
author for such an arrangement in connection with the
S.U. carburettor which is particularly adapted for such a
device. In order to carry this into effect, a separate needle
carrier is provided, concentric with the usual spindle hold-
ing the weighted piston, this carrier being extended

fldjushntnf - plunger worked by Bowden-wire
1 from Seat or Dashboard

Rocking lever eflgaginj adjusting-plunger
at orte end, and controlling needle at
the other end , by jiiiali stud engagmi
in groove in tolfar

Screwed Carrier
supporting needle

fcrh collar adjusfablij.scrcwd on to
needle carrier

Ptstoo connection ho oiifsidc of Spinning
communication movement of air piston
to Rocking Lever.

Fill. 32. — S.U. with Brewer's Patent Adjustment.

outside the top of the instrument, and actuated by a lev™
supplied with an obliquely acting control slipper. A
straight movement of this slipper enables the needle
position in the jet to be varied both for starting up, giving
a richer mixture, and in running until the carburettor is
warm. The adjustment can then be made from the driver's
seat, setting the movement back into its normal position.

By such a means the control of the S.U. carburettor
can be made ifuitable for all temperatures and fuels with-
out changing the needle.

BROWN AND BARLOW CARBURETTOR

165

The Brown and Barlow 1913 type of carburettor is
of very simple construction, and its principle of working
consists in there being two main jets and a pilot jet, the
two main ones being brought into action in turn by the
movement of the throttle, the pilot jet always remaining in
operation even when the throttle is nearly closed. These
main jets consist of two small apertures, each one covered
by a sealing, which latter can be rotated for the purpose
of adjustment from zero to the full aperture of the jet

Fig. 33. — Brown and Barlow Pin Operated Type.

opening, the amount of such opening being indicated by
a suitable number. The throttle itself has a rotary motion,
and is so arranged that an additional supply of air comes
into use if required after the throttle is partially opened,
and furthermore an automatic auxiliary air valve is fitted
which is adjusted in the works before the carburettor is
sent out. The system of operation is as follows : Each
main jet is entirely independent of the other one, and
when the throttle is somewhat less than 'half open, the
primary jet, which is the one situated nearest to the float

1 66

CARBURATION

chamber, is in use, and as the throttle is further opened,
the second jet comes into operation, and this is only
actually working when the engine is required to give its
full power. In order, therefore, to set the instrument
and the jet openings, it is first necessary to so set No. i
jet that the fuel consumption is satisfactory under ordinary
working conditions ; the second jet can then be set to
give a suitable aperture so that the engine gives its best
power when the car is climbing a hill. Whatever be the

Fig. 34. — Brown and Barlow Bicycle Type.

setting of each jet, the working of the instrument
claimed to remain unchanged as regards the effect of the
aperture of one jet or the other ; that is to say, that any
adjustment of the full power jet does not in any way
interfere with the half power jet. A similar adjustment is
provided for the pilot jet, and this can readily be made
by means of a screwdriver : the adjustable jet and choke
tube form a complete unit so that they can be taken
out and replaced without altering the setting. This

CLAUDEL-HOBSON CARBURETTOR 1 6/

arrangement makes a very compact instrument, and it will
be seen that the over-all dimensions of this carburettor
compare favourably with any of those upon the market.

The float chamber of this carburettor has a loose cap
held in position by a single spring, which forms a con-
venient method of fixing the float chamber cap so that
it can be removed without the use of tools.

Messrs Brown & Barlow have for a long time been
associated with the manufacture of carburettors for motor
bicycles, and, in addition to the 191 3 model already de-
scribed for car use, they make a single jet instrument of
the type illustrated, which comprises a modulating pin with
an additional air device.

The 191 3 model is of the hot-air heated type.

Claudel-Hobson. — The Claudel-Hobson (Fig. 35) car-
burettor is an intermediate type between the " restricted
flow type " and the two-stage type to be referred to later.
In the first place, the restricted flow is obtained by means
of the shrouded jet, but in place of an obstruction in the
actual petrol passage there is an obstruction situated a
certain distance beyond and immediately opposite the jet
orifice. In the early days of carburettor development
jets were tried, provided with an obstruction intended to
reduce the efflux of the liquid fuel by interposing a resist-
ance to the issuing stream, and thus tending to throw the
liquid back upon the orifice and decrease its coefficient
of discharge. The Claudel-Hobson jet is provided with a
damping screw, with an end so shaped and so placed within
the shrouding tube that a damping action occurs which
comes into play at high rates of discharge. If a curve of
discharge from a single cylindrical orifice be studied, such
as the curves which appear on p. 59, it will be noticed
that these curves have a rapid upward trend, which
should be damped out by some extraneous means in order
to provide perfectly uniform mixtures throughout the entire
range of engine speed.

1 68

f RATION

The Clauclel jet is further discussed in other parts of
this book, to which reference should be made. M

The rotating throttle operates upon the air intake and
the gas outlet in a similar manner to that provided in the
White and Poppe instrument. There is, however, the
difference that the throttle in the Claudel instrument, as it
is gradually closed, concentrates the air stream more and

Fig. 35. — Claudel-Hobson.

more into the vicinity of the jet. By this means we have
the effect of a varying choke tube which has been tried
in the earlier patterns of carburettors, as exemplified by
the Longuemare model R, and also in the Sthenos. The
simple form of Rover carburettor, fitted with a rotary double
purpose throttle and inclined jet, also operated in a some-
what similar manner as regards the concentration of the

CLAUDEL-HOBSON CARBURETTOR 1 69

air flow into the vicinity of the jet as the throttle was
closed down.

The latest type of Claudel-Hobson carburettor differs
somewhat from the earlier ones, in that the passage through
the instrument is of greater effective area than it is nominally,
and those carburettors used on some of the racing cars
during the past season cannot fairly be compared, as regards
their size, with the ordinary standard type.

In carburettors such as the Claudel-Hobson it is some-
what difficult to take advantage of Venturi tube formation
except at or near full throttle opening, and when the author
was experimenting with this carburettor some few years
ago, it was originally manufactured in a truly cylindrical
form right through the carburettor casing. The barrel-
shaped throttle of this instrument has a parallel hole
through its normal diameter, and it was decided to cone
out the discharge side of the body to improve the car-
buration. This external coning, combined with a slight
undercutting to give an angle of entry, increased the dis-
charge rate of the instrument, and all these carburettors
are now constructed in this manner. For mechanical
reasons the bore through the throttle has to be parallel, so
the coning is not true, and, moreover, the angle of dis-
charge is usually made greater than necessary for a true
formation.

One model (Fig. 36) shows how the Venturi outlet
can be improved in shape by lengthening the body of the
instrument.

One of the features of this carburettor is the method of
hot-water jacketing the lower part, through which the
petrol passes on its way to the jet, with the result that the
viscosity of the fuel is diminished as the temperature rises.

If in working^, the temperature of the jacket water is
constant, or nearly so, at all times of the year, it is unneces-
sary to change the size of the jet at any time. In actual
practice this is a fact, and one advantage of the instrument
is that it is unaffected by changes of atmospheric condi-

I/O

CARBURATION

tions when a working temperature has been reached.
When, however, the engine starts from cold, and the

Fig. 36. — Racing Claudel.

viscosity of petrol is greater, it is evident that some small
difficulties in carburation may occur.

Practical demonstration of this is given when it is founc

DE DION CARBURETTOR

171

that the engine pulls best when the throttle is not fully-
opened ; the explanation of this fact is that it is necessary
to increase the local suction in order that the flow of fuel
should be adequate.

Ease of starting is, therefore, obtained by providing an
air shutter to increase the suction when turning the engine
by hand.

Fig. 37, — De Dion (Zenith).

The De Dion Carburettor is a modified Zenith, and
is hot-water or exhaust heated, and it will be noticed that
the air entry passage is somewhat freer than the usual
type. A notable refinement in this instrument is the
provision of a capacious fuel filter, situated below the
needle valve of the float chamber.

This filter is easily removable, consisting of a main

CARBURATION

body, a cleaning plug, a filtering gauze and a retainin
spring for the same, and a draw-off cock.

As in the ordinary Zenith, suitable plugs of cup shape
are provided below the two concentric jets and the limiting
orifice so as to catch any sediment in the fuel, which ca
thus be easily cleared.

■

Delaunay Belleville. — The object aimed at in the
design of this carburettor is the response of the engine to
the opening of the throttle, and the ease of dismantling
of the whole apparatus. Furthermore, the method of
operation and of adjustment are of the simplest kind.

Referring now to Fig. 38, the fuel enters the instrument
through the pipe A, and by way of the cock to the centre
chamber B, in which is placed a filter C. M

At the foot of the filtering chamber is a long tubular"
sump D, closed by a screwed cap and washer, so that
ample provision is made for catching any sediment which_
may enter with the fuel. ^1

It will be noticed that the fuel passes from the outside
to the inside of the filter C, and by means of the spring
closed ball valve H and the needle G into the float
chamber.

This is the type of float chamber and needle valve
referred to in Chapter X., Fig. 24, where the weight of the
float keeps the ball valve off its seat until such time as
the fuel level rises, and permits the action of the spring to
close the ball valve by releasing the pressure due to the
weight of the float.

The main jet is shown at K, and two fuel passages are
provided by J, J, one leading also to the surface carbu-
retting chamber M.

Within this chamber is the vapour jet N, in communi-
cation with the vapour tube O ; the air enters the carbu-
retting chamber by the gauze-covered orifices of circular
form, and an extra air valve T, working against the action
of an adjustable helical spring of considerable length, and

DELAUNAY BELLEVILLE CARBURETTOR

173

a glycerine clamper valve V. The additional air which
passes through the valve T mixes with the vapour rising
up the tube Q, through the air filter R, and a hot- water

Fic;. 38. — Delaunay Belleville.

jacketed throttle chamber is fitted where these mixture
pipes join at x ; a direction plate w being fitted so as to
eliminate the sharp corner which would otherwise be
presented in the flow path.

174

CARBURATION

In the section shown at 2, the passages communicating
with the surface carburetting tube O can be seen, and it is
through these passages that the mixture is led to the
engine for starting and slow running purposes.

In the section shown at 3 the full opening S from the
throttle to the main jet mixing tube Q c^in also be seen.

With reference to the accessibility of the instrument, it
will be noticed that a door L is shown covering the main
jet K, and the vapour jet can be reached by unscrewing
the cap of the surface carburetting chamber.

The automatic air valve with its damper, control spring,
and spindle are removable with the valve seating itself
when this is unscrewed. d|

This instrument comprises a certain amount of what
would be the inlet pipe in the ordinary way, and it appears
to contain a good many parts which have been eliminated
in modern practice..

The Excelsior Carburettor. — This is somewhat typical
of American carburettor design, and like many American
carburettors has a concentric float situated around the
main fuel orifice. The distinctive features claimed for this
instrument are the ball-governed Venturi tube, the clock
spring-controlled air valve, and the Excelsior formula for
setting the carburettor. J||

Referring now to the figure, it will be seen that the fuel
enters at the lower connection, and the float, which is a
spinning, directly lifts the float valve which is situated in
a removable seating in the base of the float chamber.

An adjustment can be made here so that the valve can
be set to cut off the fuel in any desired position.

The primary air enters the circular orifice at the right
of the figure, and is drawn by the suction of the motor
past the spraying nozzle located in the restricted portion
of the Venturi tube, and the amount of the opening of the
spray nozzle is adjusted by a needle valve shown in the
figure.

EXCELSIOR CARBURETTOR

175

It will be noticed that the Venturi tube has a ball
fitting in the V-shaped depression in the Venturi tube,
and is so arranged that the air passing to the engine must
flow round the ball which restricts the flow of air, thus
reducing the suction on the spray nozzle, and consequently
diminishing the flow of fuel drawn into the engine. As
the demand of the engine increases the ball is lifted by the
suction towards the larger end of the Venturi tube, thus

Fk;. 39. — Excelsior.

gradually increasing the area of the air passage, and it is
claimed that the movement of the ball regulates the
quantities of air and fuel in their proper proportions.

An auxiliary air valve is fitted, which is under the
action of a finely tempered coil spring fitted in the
cylindrical housing shown on the top of the instrument,
the degree of tension of which spring can be adjusted.
It will be seen that in the vicinity of this additional air

[y6

CARBURATION

valve is a mixing chamber of considerable capacity, so a
to provide a thorough mixing of the additional air with
the mixture passing through the engine. The throttle is
of the butterfly type, fitted with a check screw. A special
feature is made by the manufacturers of this instrument
with regard to the construction and design of the spring
used for the additional air valve. The movement which is|||
imparted to this spring by the valve is multiplied, so that
the tension of the spring can be extremely light when the
valve is closed, and this tension increases rapidly as the_.
valve opens.

The Everest Carburettor. — This carburettor is a very
interesting example of a single lever or progressive type
of instrument, its chief attraction being extreme simplicity
and the wide range of adjustment. In its main features it
is similar to many other of the single lever type, in that
the air inlet to the carburettor, the gas outlet, and the jet
exposure, are all increased or decreased simultaneously as
the throttle lever is moved. The carburettor itself is fitted
with a main jet tube A, in which fuel is maintained at a
constant level by means of a float chamber fitted with
toggle levers of the overhead type, and the level is such
that the fuel will not overflow through the vertical jet holes
drilled through the upper side of this tube.

The petrol tube A is arranged transversely in the
mixing chamber B, from which gas passes out by the
connection C to the engine, which is situated in a practically
straight line with the opening D, and within the mixing
chamber is a sliding piston, the lower edge of which, E,
controls the air inlet, and the upper edge F controls the
gas outlet, the piston being actuated by a suitable lever G.
The piston throttle itself is fitted with sleeve II, so that
when the throttle is moved to the right to open the
passages C and D, a greater length of the jet tube A is
uncovered, thus exposing the jet orifices in proportion as
the carburettor opening is increased.

EVEREST CAKHURETTOR

177

It will be noticed that the sleeve H is not directly
attached to the piston, but is fitted to an intermediate
sleeve J, connected by a peg K to the piston, so that when

HZ.W

Fig. 40. — Everest.

the sleeve H is screwed further into or out of the sleeve j,
its position relatively to that of the air sleeve can be
changed. It will, therefore, be seen that in the general

Fk;. 41. — Everest.

arrangement this instrument is somewhat similar to the
Polyrhoe, and can be adjusted so as to give any desired
initial lap of fuel opening, but in this case the jet holes
12

178

CARBURA.TION

can be increased as desired to give any required propor-
tions of the mixture at various positions of throttle open-
ings ; for instance, a rich mixture can be obtained for slow
speed running, and a weaker mixture for intermediate
speeds, by suitably placing the jet holes. ^^1

Facile. — The Facile (Fig. 42) is one of that type of
carburettor in which the movement of the throttle pro-
duces a variation of the air inlet ports, and at the same time
regulates the discharge of petrol from the jet orifice. The
regulation of fuel discharge is performed by placing a
direct obstruction immediately above the orifice, at a
greater or less distance according to the amount of petro
required.

In the past various devices, such as a cap or an atomis-
ing cone, have been tried for this purpose, but in the Facile
carburettor a swinging, eccentrically-shaped arm is situated
in such a position that as the throttle is opened the distance
between the jet orifice and this arm increases, owing to the
eccentricity of the periphery of the arm. It is claimed
that by this means the jet is controlled as to its dis-
charge, and the fuel is more completely atomised. This
instrument differs in principle from any of those which
we have had under consideration, as although the depres-
sion in the instrument is not by any means constant, the
petrol flow is partially regulated throughout the whole
range of throttle opening and engine speed. The word
" partially " is justly used, because it has been found in
practice, and is more or less a well-known fact, that the
position of an obstruction outside the jet orifice does not
have a very marked effect upon the petrol discharge.
True it is that in a jet of the Claudel type the correct
distance between the jet orifice and the baffling screw
should be carefully observed, but as a means of regulating
the flow, one cannot usually recommend throwing the
petrol stream back upon itself We know that if a jet
orifice is placed in a vertical position, and that, say, water

FACILE CARBURETTOR

1/9

issues directly from it, the falling globules tend to lessen
the rate of discharge by striking the issuing stream.
In a carburettor system one would suppose that the
velocity of air carried with it the atomised fuel, and the
fuel would be effectively removed from the vicinity of the
jet and thus not have any baffling action. In the Facile
carburettor arrangement the swinging quadrant can only,
therefore, be considered as a valve whose lift can be varied

Fig. 42. — Facile.

in a very neat manner. Supposing, now, that the car-
burettor is set for its slowest running position, the quadrant
will be swung down by the throttle, and the distance above
the jet orifice can be regulated by altering the distance of
the jet itself In order to do this a spanner can be inserted
through a small slot in the side of the instrument, and the
jet turned bodily round so as to screw it up or down by a
small amount. This can, of course, be done when the car

l8o ^HP CARBURATION

is running, and no locking nut is required. At the other
end of the range an adjustment of the quadrant is possible,
there being a small nut projecting through the side of the
throttle chamber which operates directly upon the location
of the eccentric arm, thus making the eccentricity variable.
Between the points of maximum and minimum duty, the
intermediate positions will be practically self-adjusting,
provided always that the range of working of the instru-
ment is along a straight portion of a fuel discharge curve
from the particular instrument. If this is not so, the air
ports could be suitably shaped to comply with any par-
ticular conditions, so that if a small instrument were used in
connection with an engine of large capacity, a big depres-
sion could be prevented by providing air ports of sufficient
size, which could come into use only when the throttle was
full open, and the engine running all out.

G. and A. — The G. and A. carburettor (Fig. 43) exempli-'
fies one of the earlier attempts in carburettor construction to
permit working at a more or less constant depression where
the action of gravity is employed against a moving weight.
This instrument does not naturally work at a truly constant
pressure difference, but the variation at higher engine
speeds is less than it would be in a fixed jet and choke
tube type on account of provision being made for an addi-
tional air supply to the mixing chamber. In the G. and
A. system a conical choke tube is provided with an inclined
jet at its throat, the inclination being of the order of 45
degrees to the vertical, and by this means it becomes pos-
sible to remove the jet when a plug situated opposite to it
is withdrawn, a special tool being provided for this purpose.
The conical choke tube extends well up into the mixing
chamber, and round the base of an annulus in this chamber
a number of holes are drilled of different sizes, which
are covered by balls of various sizes, held in position by
a cover plate, and as the suction increases so the balls rise
from their seats, allowing an additional supply of air to^

G. AND A. CARBURETTOR

l8l

The mixing chamber contains

enter the mixing chamber,
a throttle, which may be either of the rotary or piston type,
and the sides of the chamber are hot-water jacketed for
use in a motor car, but for aviation purposes this carburettor
is generally used without a jacket : the air enters a bell

(Q) ,,

Fk;. 43. — G. and A.

mouth at the lower part of the instrument, and has a
straight through path. The carburettor itself has the
merits of simplicity, and has proved quite satisfactory in
many cases where it has been employed. It will be seen
that in the lower limits of working the air velocity past the

l82

CAkBURATION

jet is comparatively small when the choke tube is made
sufficiently large to work efficiently at high speeds, and,
furthermore, it will be noticed that the supplementary air
supply does not come into contact with the petrol spray.
As the ball seats are unprotected from impurities in the
air, they may possibly become fouled, and a certain amount
of care should, therefore, be taken in fixing this instrument,
so that it is not unduly exposed to external interference.

Holley. — The Holley carburettor is manufactured in
large quantities in America, and has been seen here on the
Mitchell and Ford cars. This instrument in the modern
type differs from a number of American carburettors in that
there is no supplementary air valve, and it is claimed that
the shape of the jet of itself prevents an excessive flow of
petrol when great differences of pressure exist in the
instrument.

This regulation is due to the fact that a certain amount
of air is allowed to pass through the cup-shaped nozzle as
the level of the fuel in the float chamber falls when the
demand of the engine is great. By means of a small tube,
not shown in the drawing, communication is made between
the annulus round the outside of the cup-shaped jet and the
inside of the float chamber above the level of the fuel under
high speed working conditions. The direct fuel communi-
cation between the float chamber and the jet is through the
small drilled plug, and it will be seen that there are two
separate channels in the sides of the fuel nozzle through
which either petrol alone or petrol and air are allowed to
pass. At low speeds no air passes through the jet, but as
the speed increases the upper orifice becomes uncovered
owing to the fuel level falling, and air thus enters the two
slots in the side of the jet tube together with the petrol.
In this arrangement there is undoubtedly a certain amount
of baffling action by reason of the shape of the jet orifice,
which causes an obstruction to the free flow of the fuel.
Furthermore, the presence of the air would still further

HOLLEY CARBURETTOR

183

retard an abnormal efflux at high speeds. This instrument
has been developed to work at engine speeds between 200
and 2,000 r.p.m., and a test on a Reo car with four

Fig. 44. — Holley.

cyHnders 4 in. diameter and 4.5 in. stroke, with a gear
ration of 3.7 to r, gave fuel consumptions as follows : —

At 15 m.p.h. 19.2 miles per gallon.

j»

19.2

»j

17-5

15-5

»)

14.0

Looking now at the power developed with this engine,
this was as follows : —

600

r.p.m.

13 B.H.P.

800

200

27-5 »

600

1 84

CARBURATION

These powers, of course, are not high as compared with
modern European practice, but up to the speed mentioned
the power curve progresses in a straight line.

The Ideal Carburettor has the following characteristics.
The fuel stream is at right angles to the air stream, the
former being in a thin film with a constant orifice co-
efficient. The jet is rapidly adjustable for fuels of different
density, and the adjustment can be accurately made by
a micrometer screw head ; furthermore, the jet can be
easily dismounted without the use of tools. The fuel is
automatically cut off when the engine stops, and the
suction cannot exceed 7 in. of water head.

Fig. 45 shows a longitudinal section through float
and mixing chambers. A is the float chamber in which
the level of fuel is controlled by an inverted needle valve
B and float C, which is provided with a simple locking
device D for adjusting level of fuel to compensate for
varying density of spirit and wear in the valve or seat.
The float chamber is provided with a self-locking and
readily detachable cover E. In the base of the float
chamber is a large circumferential filter F, which is a
light friction fit, and removable by the fingers. The
float chamber is cast as an integral part of the bottom
cover or jet base G, and is connected to the base of the
mixing chamber of the main carburettor casing H, in
such a manner that it may be rotated and clamped in
that position which is found to be most suitable to
any engine. Mounted concentrically at the base of the
casing H is the air intake sleeve I and flange L, the
former being in two portions, and capable of being
rotated to any position. M is the fuel spraying jet,
which is of special construction, and is provided with
a conical ground seating, permitting its rotation to the
most suitable position for observing and setting the
graduated micrometer scale. N is the zero scale, which
is held by a sunk screw, thus enabling its position to

IDEAL CARBURETTOR

185

be adjusted should the jet edges be accidentally damaged.
O is the movable scale, permitting the adjustment of the
area of the jet to be varied in increments of TiiiiFiy o^ ^
sq. in. per scale division. The jet orifice consists of an

annular circumferential opening formed by the jet body,
and a movable cap controlled by the small scale O,
whereby the width of the annular opening can be varied.
The complete jet M can be instantly removed by depres-
sing with a slight side movement the small lever P, which

1 86

CARBURATION

may be effected with one finger, thereby allowing the
jet to drop. The replacing of the jet is as simply and
rapidly effected.

Surrounding the said jet M is the fuel sleeve Q, sus-
pended from the cross pin R, which in turn is fixed to

Fig. 46. — Ideal.

the gravity-controlled air sleeve S. The fuel sleeve Q
is provided with two triangular slots, the apex of each
being slightly below the level of the jet opening when
the engine is at rest. As the sleeve Q is raised, an
increasing length of the circumferential strip of the jet ■

IDEAL CARBURETTOR 187

is uncovered by the triangular slots. The gravity-con-
trolled air sleeve S is adapted to regulate the air opening
fornried by the sleeve S and the casing H at the point T.
At the lower end of sleeve S, and concentric with jet M
and fuel sleeve Q, is a small annular initial air passage U,
tapering outward at the top and bottom, and having at
its base a number of transverse openings V, communicat-
ing with the opening in the air inlet flange L by the air
passages w, formed at the base of the main casing H.
At the upper end of casing H a cylindrical throttle valve
is provided, so constructed that it gives a vacuum-braking
effect when the throttle is fully closed, and a filtered air
scavenge beyond the full throttle position. The throttle
lever is secured to its spindle by a split-coned boss and
coned clamping nut, enabling the lever to be clamped
in the most convenient position to suit existing control
levers with the minimum of trouble. On the throttle
valve cover is a circular slot provided with adjustable
stops, whereby the air scavenge control may be entirely
cut out, or the throttle may be prevented from actually
stopping the motor, the stops limiting the travel of lever
to accomplish this.

Normally, the gravity-operated air sleeve rests on the
bottom cover, the main air passage being closed, and the
fuel being entirely cut off by the fuel sleeve. On the
throttle being opened a little, and the engine turned slowly
by hand, a small volume of air will pass through the
passage U into the mixing chamber, in which, owing to the
relatively small area of the former, a slight depression or
partial vacuum has been produced, causing the air sleeve S
and fuel sleeve Q to be upwardly displaced, first uncovering
a small strip of the jet outlet sufficient to carburate the
small volume of air passing, and then, as the speed of the
engine gradually increases, the main air opening T opens
up at the same time, proportionately increasing the avail-
able jet strip. On a reduction of throttle opening (if the
load is unaltered) the partial vacuum in the mixing

1 88 ^^^r CARBURATION

chamber will tend to decrease, the air sleeve s being
acted on by gravity will move downward, thus reducing
the area of the strip T, until the partial vacuum in the
mixing chamber is sufficient to support the sleeve, and
a reduced volume of gas will pass through the mixing
chamber in unit time. The air velocity through the
initial annular opening into which the fuel is sprayed is
constant under all conditions. The position of the floating
sleeve device is not definitely related to either actual
throttle position or engine speed alone, but depends
entirely on the volume of charge passing to the engine.
When the throttle is moved to the air scavenge position,
the mixing chamber port A^ is gradually closed, and the
partial vacuum being reduced, the air and fuel sleeves are
allowed to return to their normal position, closing the
circumferential air inlet, and positively cutting off the
fuel at the jet. While the carburettor is essentially of
the constant mixture type, up to the full throttle position,
there are times when it is desirable that the mixture
should be weakened, as when running down a gradient,
which is not sufficiently steep to maintain a good average
speed by gravity alone. This is obtained by opening the
air scavenge a little, which causes the air and fuel sleeves
to be lowered slightly, when a smaller volume of car-
buretted air will pass through the mixing chamber, and
be further diluted by the air entering through the air
scavenging inlet. This variable mixture effect, which is
in conjunction with, but is additional to, the pure air
scavenge, makes for economy during average conditions j
of running, whilst retaining the advantages of a constant
mixture for maximum power and controllability under
normal working conditions.

Kingston. — The Kingston carburettor possesses certain
well-known American features, the first of which is a
cork float, and the simple connection between this and
the needle valve. Although the cork float is scarcely

KINGSTON CARBURETTOR 189

in accordance with European ideas, it is really remark-
able how well it works. It is, of course, not liable to
be completely put out of action under ordinary usage, and
it is very cheap. The use of such a float eliminates the
necessity for small toggle levers, and it lends itself to easy
attachment directly to its lever. The Kingston carburettor
has a peculiar jet tube, forming a starting well, situated
with its upper orifice slightly above the greatest restriction
of the conical choke. A central needle is provided with
an adjusting screw and locking device, so that the amount
of petrol discharged from the orifice can be varied.
Naturally, under normal working conditions, the level of
the fuel descends in the starting well to the position of its
greatest restriction. When, however, the engine is stopped,
a small quantity of petrol can accumulate in the starting
well and be ready for restarting the engine. The main
air supply, as is somewhat common practice in American
carburettors, is led downwards through one leg of a U
tube, and, passing upwards in a vertical direction through
the carburettor, is led off at right angles through a
butterfly throttle. With regard to the principle of
the carburettor, the body of the instrument forms a
mixing chamber, and the diverging jet orifice, closely
situated in a choke tube, should give a very fine spraying
effect. Round the upper internal ledge in the mixing
chamber a number of balls are placed, somewhat in the
manner of the French G. and A. carburettor. These balls
form a means for the admission of an additional supply of
air when the engine suction is great. A somewhat curious
shape of float needle is employed, which may be advisable
on account of the large range of movement of the cork
float which is used.

The Limit Carburettor, designed and manufactured
by Messrs Morgan & Wood of Bristol, was brought into
prominence by reason of its having undertaken the first
R.A.C. carburettor trial in 19 10, and the results shown by

I90

CARBURATION

this trial were eminently satisfactory, some of the figureT
of which are given in Chapter XII. on exhaust gas
analyses. This instrument is somewhat on the lines of
the Zenith, in that it has a gauged orifice, through which
the supply of petrol passes to supplement the usual jet at
all periods of running, but it differs from the Zenith type
of instrument in that the additional fuel supply is made
after total or partial evaporation. This evaporation is said
to be a great advantage, in that the requisite amount of
fuel is delivered when the suction would be insufficient to
operate this quantity of fuel, and in addition there is no
accumulation of unevaporated fuel in the carburettor under
slow running conditions. Referring to the drawing, a
gauged orifice A at the bottom of the limiting tube B is
not affected by the suction of the engine, for the tube B is
open to the air at the upper end, thus the amount of fuel
supplied to the engine from this source is limited by the
head of the fuel in the float chamber. The main jet G is
fed by fuel in the ordinary way. When the engine is
stationary the fuel reaches a level in the limiting tube,
which is practically the level of the top of the float, and
this level is such that the plug D is surrounded by a film of
fuel. When the engine is started, the suction takes effect
upon this head of fuel, in addition to the jet G, by way of
the orifice L, and the passage F of annular formation, but
after the engine has been running a few minutes the excess
of fuel available for starting is completely exhausted, and
the flow of fuel to the engine is then confined to that
through the orifice A and the jet G.

Henceforward a rich mixture for slow running passes
up the passage F, and is augmented by a normally weak
mixture by way of the choke tube H and the vaporising
spiral J from the jet G, and these two mixtures compensate
each other and provide a correct mixture. The main jet G
is so set that it cannot give a rich mixture at any speed,
and the limited supply through the orifice A is set exactly
to compensate this mixture to any strength required.

LIMIT CARBURETTOR

191

Now the difference between this type of instrument and
the Zenith type is that the fuel which passes through the
limiting orifice A also is led through an evaporating
chamber in which is situated a hollow plug D, and hot
water from the engine circulates inside the plug, outside

Fk;. 47. — Limit Carburettor.

the chamber, and also inside the water jacket of the mixing
tube J. The plug D has an additional heating surface
formed upon it by means of a long external thread which
is cut upon it, and it is plain that the fuel passing through
this vaporising chamber is evaporated on its way to the
passage F.

192

CARBURATION

Longuemare. — This make of carburettor was one of;
the very earHest on the market, and is, as its name suggests,
of French origin. Since the earh'er types, which have been
well known to pioneer motorists, the design has not been
allowed to stagnate, but has progressed in accordance with
modern ideas. The latest type of Longuemare may be said
in a great measure to embody two important principles,
which appear as original in the Zenith and Claudel types.
Considering the throttle first, this is of the barrel type, but,
as a difference from the Claudel, the supply of fuel for slow
running passes through a small hole on one side of the
throttle barrel, and outwards towards the engine through

C*^rC^'^-(

Fk,. 48. — Longuemare.

a notch on the other side of the throttle barrel. The jet
arrangement in this instrument has several important
features which are well worth detail consideration. The
presence of a slow running jet immediately beneath the
throttle has been referred to, and the supply of fuel to this
jet is by means of a concentric tube arrangement, the inner
tube supplying petrol through a small jet standing up in
a well, to which a regulated air supply is admitted, a thumb-
screw and needle valve adjustment being provided for this
purpose. In closed throttle position, owing to the throttle
valve fitting down on the top of this well, any desired
mixture strength can be produced.

At the supply end of this supplementary fuel system

LONGUEMARE CARBURETTOR IQS

another adjustable needle valve is fitted, but the capacity
of this orifice is sufficient for the maximum demand of the
engine, and, therefore, when the slow running supply only
is in use, the surplus fuel rises up in a reserve well round
the fuel regulating needle.

At any particular time, when the throttle is fully opened,
this reserve of fuel is free to pass through the main central
passage and the main jet in order to give the engine the
necessary pick-up when the depression on the carburettor
is small. We will now consider the main fuel jet, which in
a measure follows the well-known Longuemare pattern.
There is an important modification, however, in that the
efflux of fuel from the orifices in the main jet is deflected
by a small cover plate, so that the fuel stream meets the
air stream at right angles. Reverting again to the float
chamber and the reserve fuel supply, it will be evident
that, as the central tube in the float chamber becomes
depleted of fuel by the initial drain upon it when the
throttle is fully opened, there will be here a means of a
constant air leak through a series of holes in the top of the
tube surrounding the needle valve adjustment. In practice,
air is allowed to leak through these holes, and to pass
downwards through the petrol passage and through the
main jet of the carburettor. A claim is made that by
allowing a small proportion of air to pass actually with
the fuel through the jet orifice, a perfect spraying and
intermingling of the fuel with the air is obtained.

The Mayer Carburettor. — This is an American instru-
ment which has been on the market for some years, and
its principal feature is that of simplicity. Like the
majority of American carburettors, the Mayer is fitted
with an extra air valve, and it has also two jets. The air
supply is heated. One important feature in connection
with this carburettor is the dashpot air control to prevent
the air valve fluttering ; the air intake pipe is so arranged
that both the main and the auxiliary air draw their supply

»3

194

CARBURATION

from the same source. For the sake of easy starting an
air throttle is fitted at the carburettor entrance to this air
supply, so that the suction upon the jets can be increased
when turning the engine by hand. It is claimed that the
effect of the dashpot upon the air valve retards its action,
so that as the throttle is suddenly opened when it is desired
to accelerate the engine, the momentary suction upon the
jets is above the normal, and increases the flow of fuel

Fig. 49

before the additional air supply is added. The auxiliary
air valve then opens slowly and steadily till it reaches its
correct lift, which is governed by the spring.

Referring now to the two jets in the instrument, it will
be seen that one is covered by a ball valve and the other
has a free outlet, the latter one being the slow running
jet. As soon as the engine suction increases to a certain
amount the ball valve rises from the second jet and allows

NAPIER CARBURETTOR I95

it to come into operation. The principal adjustments in
connection with this instrument are made by means of the
additional air valve and the needle valve operating the
main jet, and by means of these two a sufficiently accurate
adjustment can be made for all ordinary purposes.

It will be noticed that the float chamber is of the
concentric type, but the method of operating the fuel
needle is somewhat unique, and very simple.

Napier. — A simple form of the varying jet orifice is
embodied in the Napier design of carburettor for their
larger engines. In this instrument the nozzle is of cylin-
drical form with a flat upper end, and in this end there are
two apertures, one consisting of a small hole, for slow
running, and the other of a narrow segmented slot. The
top of the jet is covered with a cap, also provided with a
slot, so arranged that the cap can be rotated when in
position and the slots before-mentioned made to register
with one another more or less. In this arrangement the
cap is connected to the throttle and opened with it. In
order to compensate for increased engine speed with a
fixed throttle opening, a diaphragm-controlled extra air
device is provided, the diaphragm acting upon a cylindrical
shutter which uncovers triangular ports.

There are several types of carburettor fitted by the
Napier Company to their different sizes of car, and these
types vary in principle as well as in dimension. The later
model, as fitted to the 15 H.P., is of the two-jet type, there
being a slow running jet situated in a conical choke tube,
and beside it a jet of similar shape but of larger dimensions,
which comes into operation at about one-half the throttle
movement.

These jets are situated immediately below the barrel
throttle, and the throttle itself being hollow forms a mixing
chamber. In it are two apertures : the larger one, of
elliptical shape, traverses over the slow running jet, and a
circular opening traverses the main jet. It will thus be

196

CARBURATION

seen that the first movement of the throttle enables one jei
only to work, and during the second half of the movement
the two jets supply the fuel. The control of the mixture to
the engine is carried out by means of an opening on the
upper part of the throttle barrel, this opening having a

Fig. 50. — Napier

narrow slit extending at one side of it for the purpose of
accurately checking the flow of mixture at low engine
speeds. This slit gradually widens out until it gives full
throttle opening. The air enters the carburettor in a
vertical stream, the lower part of the instrument being
provided with a large pan-shaped gauze to exclude foreign

NEW MILLER CARBURETTOR I97

matter in the air. The type of instrument used for the
larger models is fitted with a sleeve round one of the jets,
mechanically connected so that it can be raised to close
the area of the choke tube for slow running. Another
type of carburettor fitted to the 45 H.P. Napier has a
hydraulically controlled air valve ; the pressure of the
circulating water acts upon a diaphragm, so that as the
engine speed is increased the main air supply is also
increased. In this type of instrument it will be seen that the
carburation depends in a measure upon the efficiency of
the water pump, which would appear to be not altogether
satisfactory, as a delicate instrument like a carburettor
should either be an independently operated unit or in itself
automatic.

The New Miller Carburettor. — This instrument is
of American design and manufacture, and comprises
several interesting features, the principal of which is the
interconnecting of the fuel needle and the extra air device
with the throttle. Referring to the figure, it will be seen
that there is an internal piston attached to the butterfly
throttle which in movement uncovers air ports situated in
the mixing chamber of the instrument, and, simultaneously,
by means of a lever arrangement, the fuel needle is with-
drawn from the orifice in the jet.

This carburettor is designed with a normal air aperture
round the fuel nozzle, the auxiliary air being taken through
an annular opening, and the proportion between the two
is so arranged that the correct amount of vapour is supplied.
In order to increase the richness in the mixture the position
of the taper needle in the nozzle can be altered from the
driver's seat by means of a suitable device, so that the
proportions of air always remain unchanged, and the fuel
can be increased at will according to weather conditions
and grades of fuel.

Another feature of this instrument is that the air
ports, when open, allow an unrestricted passage for

198

CARBURATtOlSI

the air. The air enters through an annular opening, thus
eliminating a deflected charge. The needle and nozzle are
in the centre of the instrument, so that an evenly dis-
tributed mixture is ensured, and the throttle is attached
to the air sleeve giving a positive air opening. Another

Fig. 51. — New Miller.

important point in connection with this instrument is the
mechanical control of the fuel needle, making the whole
instrument positive in operation.

It will be noticed that this carburettor is of the con-
centric type, and a glass float chamber is fitted in the base,

PLANHARD CARBURETTOR I99

the float chamber itself being maintained in position by
means of a screwed cap fitted on to the lower part of the
instrument.

It has been mentioned before that the fuel adjustment
can be made from the driver's seat, and this is a most
important feature, as it is the only adjustment required
when the instrument has once been fitted on to the engine.

The needle valve is actuated by a cam mechanism
operated by the throttle, and a spring is fitted in the needle
valve housing, so that the point at which the needle com-
mences to lift can be adjusted.

Every care is taken in the manufacture of this
carburettor, and it certainly appears a free design, with
the exception, perhaps, of a multiplicity of moving parts,
and the obstruction of the passage of the gas to the
carburettor, which exists by reason of the crosshead in
the air piston and the linking motion to the butterfly
throttle.

Planhard Carburettor. — A radical departure from the
usual type of carburettor in a number of ways is made in
the improved Planhard carburettor, made by the Planhard
Manufacturing Company, 1784 Broadway, New York, and
Kokomo, Indiana. The principal differences are in the
small number of parts and an entire absence of springs,
levers, and cams. This instrument is of the concentric type,
the float chamber surrounding the mixing chamber, and is
designed in such a way that all joints are in a horizontal
plane, and it may be assembled by screwing the central
member into the top member.

The proper vaporisation of fuel and its thorough mixing
with air to form a correct explosive mixture is well arrived
at in the new carburettor of the Planhard Company in its
new double concentric air and mixture tube construction.
The fuel nozzle is in the centre of the carburettor, and it
is entirely surrounded by the fixed or constant air tube.
This is contracted at the upper end above the nozzle.

200

CARBURATION

Surrounding this tube, between it and the float chamber
wall, is the annular opening through which the auxiliary
air is admitted.

This is a most important feature, as the columns of
mixture and auxiliary air always travel in the same
direction. The auxiliary air surrounds the mixture as it
leaves the contracted tube, and acts as an envelope to
insulate the mixture from direct contact with the cold walls
of the manifold, where it might condense. This surround-

FiG. 52. — Planhard.

ing envelope of pure air gradually unites with the inner
column of rich mixture until, before reaching the cylinders
of the engine, the auxiliary air has thoroughly vaporised
fuel in suspension. A dry, rapidly burning mixture is
thus produced, and it is claimed that the greatest possible
amount of power from a given amount of fuel is obtained.

The auxiliary air is admitted to the carburettor through
a series of ball valves. These are seated in holes in an
adjustable screw plate at the bottom of the auxiliary air
tube. The ball seats vary in size. The bronze balls are

POLYRHOE CARBURETTOR 201

all of the same size and weight, and are thus lifted from
their seats progressively as more auxiliary air is required.
The ball on the largest seat is lifted first. These balls act
differently from a single auxiliary air valve, which con-
stantly flutters, and, therefore, changes the amount of
auxiliary air admitted to a considerable degree from the
correct amount. The ball valves used in the Planhard
carburettor each lift a distance about equal to that of the
lift of a single auxiliary air valve, but as these balls lift
progressively, their total travel amounts to six or eight
times that of a single valve for the same function. The
balls do not flutter, and on account of their range of action
they are not delicately poised, and, therefore, give for vary-
ing engine speeds a uniform amount of auxiliary air.

The spray nozzle is cup-shaped, and when the motor is
standing idle this fills with fuel to within a short distance
of the top, and acts as a priming device, thereby making
the starting of the motor easy. The float chamber is pro-
vided with a flooding device and a vent. The air pan at
the bottom of the carburettor is secured by a wing nut,
which also serves for clamping the adjustable auxiliary
ball plate, which is knurled on its periphery, so that the
lift of the auxiliary ball valves may be quickly and easily
adjusted, whereupon the plate is locked by the wing nut.

The Planhard carburettor is of exceedingly robust and
simple construction, and embodies in one unit not only
several standard features of carburettor construction, but
such special ones named above. One noticeable feature is
the very simple method by which the float actuates the
needle valve, also the removable needle valve seating.

Polyrhoe. — The Polyrhoe is of the constant suction
automatic type, and is so arranged that the row of
jets is situated slightly above the level of the petrol in
the float chamber. The difference of pressure under
which the instrument works is just sufficient to cause the
petrol to flow from those jets which are in operation, and

202

CARBURATION

to spray it effectively. The operation of the instrument is
as follows : In the throat of the instrument a piston
works against the action of a large spring, the total range
of working being only a portion of the total range of the
spring, thus errors due to spring action are practically
eliminated. As the demand of the engine increases the
piston recedes, carrying with it a tongue piece which travels

Fig. 53. — Polyrhoe

over the jet orifices in such a manner that all those orifices
situated above the air inlet orifice are directly acted upon
by the suction produced. The remaining orifices com-
municate with the surrounding atmosphere, but being out
of line of direct suction, no petrol is caused to flow from-
them. It will thus be seen that for any one position of
the air piston and tongue piece there is a direct relation

POLYRHOE CARBURETTOR 203

between the area of the rectangular air slot and the com-
bined area of the numerous petrol orifices.

Now, in order to alter or vary this relation, the air
orifice only requires attention, and for that purpose a slide
is provided, whose movement is in a direction at right
angles to the direction of movement of the air piston.

This slide is actuated by means of a Bowden wire from
a lever controlled by the driver ; thus the proportions of
the mixture can be altered at will by the driver at any
time whilst the car is running. It has been shown that for
slow speed running and starting up a mixture somewhat
richer than the normal is required ; this is on account of
the fact that incomplete combustion usually occurs under
such conditions. To comply with this necessity, it is only
necessary in the Polyrhoe carburettor to arrange the air
slide so that some of the jets are open when the air slide
is shut, and that, at small openings of the air slide, there
are always that same number of petrol jets operative in
excess of the correct number. As the air opening
increases, the ratio of these extra jets to the total is so
small that the effect of their operation becomes negligible.
A circular or drilled jet orifice is extremely difficult to
manufacture accurately in small sizes, a drilled hole of such
dimensions is seldom round, and a series of such holes
cannot be guaranteed to be of exactly the same size. For
this reason the Polyrhoe jets consist of a number of slits
in thin metallic foil clamped together in five layers. The
slots in the various layers are staggered, so that the effect
in actual working is that of a continuous and uniform jet
opening. The disposition of these jets is such that the
incoming fuel becomes intimately mixed with the air, and
a perfectly uniform charge results.

As practically the whole of the evaporation of the fuel
in this carburettor takes place at the air throat, the neces-
sary heat need only be supplied to the carburettor body,
and for this purpose a hot-water jacket is fitted. However,
this instrument can be more easily started from cold than

204

CARBURATION

many others, as, on account of the adjustable air slide,
more fuel in proportion to the air can be allowed to pass
to the engine in the initial stages when the heat is not
sufficient, nor the temperature high enough to vaporise the
heavier fractions of the fuel. When, however, normal
working temperature is reached, the air slide can be opened
and an economy in fuel effected. We all know the diffi-
culty in running a correctly adjusted carburettor for the
first few minutes when cold, and such a difficulty can be
overcome when an accurately marked position for the
normal adjustments is provided. By these means the
instrument can be thrown out of true adjustment for the first
few minutes as shown.

It is interesting to note the very small percentage of
carbon monoxide in the exhaust gases of an engine tested
with this carburettor, for it never exceeded 0.2 with the
engine loaded, and 0.8 with the engine running light. J

During these tests the proportion of CO.2 varied from
13.4 per cent, to 13.8 per cent, when loaded, and from 13.2
to 13.5 per cent, when light, the consumption of spirit of
0.760 sp. gr. being at the rate of 45 ton miles per gallon on
the track at a speed of 20 miles per hour.

The " Rayfield " Carburettor, manufactured by the
Findeisen 81 Kropf Mfg. Co. of Chicago, has been very
successful in America, especially in connection with
racing cars.

The principles of operation of this instrument are
that it combines both the automatic and mechanical!
means of control, and that the needle valve is lifted,
and the mechanical air valve raised proportionately as
the throttle is opened. In addition, an automatic air
valve supplies such air as is not admitted by the
mechanical air openings. |

^ At low speed, both the fixed and mechanical valves are
completely shut off, giving a very small volume of air,
which passes through a choke tube at the side of the fuel

RAYFIELD CARBURETTOR

205

nozzle, and consequently the motor can be readily throttled
down.

At high speed, however, all the air openings are in
operation, thus giving a very free access of air to the
mixing chamber, with the result that the depression in this
chamber is smaller than that usually obtained.

The adjustment for low speed running is obtained by
rotating a screw which raises or lowers the needle valve
to give the required mixture, while the high speed adjust-

FlG. 54. — Rayfield.

ment moves a cam forward or backward, giving more or
less lift to the needle valve as the throttle is opened. In
addition to these two adjustments there is one for the
air valve for intermediate speed.

It will be noticed that the Rayfield carburettor belongs
to that class in which the flow of fuel from a single nozzle
is controlled by a needle valve in connection with the
throttle, but in addition to the usual interconnection one
sees that the main air entrance is closed by an additional

206

CARBURATION

throttle which is linked to the main throttle in the mixing
chamber.

The movable needle is held towards its seat by a spring
of the spiral type placed above it, and is operated by a^\
small arm interconnected with the throttle mechanism.
The link motion operating the valves can be adjusted,
so that the correct proportions of the air and fuel can be
arrived at. I

The Rayfield carburettor has a float chamber of un-ll
usually large dimension, the float being of metal, operating
through a lever upon the needle valve, below which is
placed a large strainer. Admittance of fuel to the mixing
chamber is through the centre of the nozzle, which is
opened and closed by the needle, the lower end of this
nozzle communicating with the fuel chamber by means of
a series of holes.

It will be noted that in the action of this instrument
direct mechanical means are principally employed, and it
is necessary to pay attention to three distinct adjustments
in order to effect proper regulation, but when once made
require no further attention. This is naturally a somewhat

difficult matter for the ordinary motorist to undertake, and
to the European mind it appears unnecessarily complicated.
There is still one further difficulty or departure from
what is now standard practice, in that the air for carburation
does not all pass the jet, in fact only a small portion of it
comes in any direct line between the jet orifice and the
throttle valve.

Schebler (Fig. 55). — Here we have one of the simplest
arrangements, which, moreover, works in a satisfactory
manner. Not that this carburettor has any particular
claims from a scientific point of view, but in its country
of origin fuel consumption is of minor importance. The
instrument is made in several forms, but the principle
is the same — a single fuel jet, with variable suction
up to a certain point, then an unstability of affairs as ai

SCHEBLER CARBURETTOR

207

spring-actuated air valve is allowed to open. There is
a distinction, however, in this carburettor as compared
with the older types of well-known spring-controlled air
valve instruments, in that the extra air is admitted on the
atmospheric side of the jet, and not to the carburetted air
stream between jet and throttle.

In the Schebler carburettor a small air aperture is pro-
vided of I in. to h in. diameter, say at right angles to the

1 W-1

Fig. 55. —Schebler.

main mixture pipe, and in the bend of the carburettor a
single jet is screwed, say at an angle of 45°. The jet may
be situated in a vertical position in the bottom of the
carburettor with a small air aperture round it. As the
engine speed increases the air velocity increases in the
ordinary way until the depression inside the instrument
reaches a certain value. At that time a spring-actuated
air valve opens and admits an additional supply of air,

2o8

CARBURATION

which is allowed to cross the jet, and from that moment
it is difficult to state exactly what are the conditions of
pressure and air velocity inside the instrument. These
conditions will depend upon the tension of the spring and
the shape of the air passage, and may be varied at the will
of the driver, but he has of necessity to descend from his
seat and make any adjustments directly by hand. A small
flap is usually provided to close the whole of the air intake ..
for starting. The throttle is of the butterfly type. ll

As this American carburettor has been much im-
proved by means of the addition of an adjustable and
variable fuel nozzle, it will be as well to give it further
consideration. The Schebler carburettor is primarily
fitted with an inclined nozzle, entering the aperture of
which is a needle with a very steep taper. This needle is \\
directly operated by the throttle, and its movement can
be regulated at three different points. The actuating
mechanism consists of a bell-crank lever, which works
with a partially rotary motion, so that a small projecting
arm attached to the fuel needle traverses a cam-shaped
path. For adjusting the slow running position the needle
itself can be moved upwards or downwards in the jet
orifice by means of a milled head, and when this adjust- ij
ment is made, the throttle can be opened. The projecting
arm on the fuel needle then traverses the cam-shaped
path, and the needle itself is raised by the small spring
shown, the amount of lift being regulated by the contour
of the path on which a small roller runs. This path is a
piece of flexible metal, and it is adjustable at its middle
and remote positions by means of two quick pitch screws
fitted with dials. In order, therefore, to give a greater or
less effective area to the jet at any point it is only necessary
to rotate the dial fingers in one direction or the other.
These fuel adjustments, it will be noted, depend entirely
upon throttle opening, and have no relation to the demand
of the engine at any time. It is, therefore, necessary to
combine some form of air regulator, and this is done by

SCHEBL£R CAkBURETtOR 269

the adoption of a spring-actuated air valve, through which
the whole of the air passes. The Schebler carburettor,
like several other American types, uses a leather valve for
this purpose, and this valve is first set by making it seat
lightly when the throttle is almost closed and the engine
running slowly. Obviously such an arrangement, though
convenient in some respects, cannot be considered in the
same class as a modern European carburettor as regards
automaticity of action, too much dependence being made
upon the action of the air valve. The carburettor, however,
is fairly easy to adjust from time to time.

The Latest Type. — The new Schebler model " O " differs
from all previous Schebler carburettors, in that two spray-
ing jets or nozzles are used, one being the main jet
located in the Venturi air passage, which is concentric
with the float chamber, and the second jet which is fitted
higher up in the wall of the carburettor. The secondary jet
is under the control of a plunger valve, which is raised from
its seat by the suction of the engine, and only comes into
operation after an engine speed of about 800 revs, per min.

The operation of the instrument is as follows : After
a speed of 400 revs, per min. has been obtained, the
auxiliary air valve commences to open, and is in operation
in speeds of from 400 to 800 revs, per min., and above
this latter figure the auxiliary jet comes into play, this jet
being situated in a small pocket between the operating
valve and its seating, when the former is raised by the
engine suction.

The air for this auxiliary mixing chamber enters
through a port in the casting leading to the outside
atmosphere.

This instrument is hot- water jacketed, and is fitted with
an air shutter to facilitate starting.

Scott-Robinson. — The Scott-Robinson (Fig. 56) con-
stant suction carburettor has been on the market for some

210

CARBURATION

years, and though at first sight it may appear somewhat
similar to other instruments discussed, yet it embodies
several interesting features. In the first place, although
the jet orifice is controlled by a modulating pin, the flow is ll
not directly acted upon by the air stream, but there must
of necessity be a certain amount of lag in the action of the
instrument due to indirect suction. An important feature
of this carburettor is the perfection of the dashpot, with

Fig. 56. — Scott-Robinson.

which all constant suction instruments must be provided
to ensure effective working, and in the Scott-Robinson this
adjunct is probably the best we have come across. Con-
sidering the carburettor in detail, the action depends upon
a moving part controlling air and fuel flow, and operating
between gravity direct on the one hand and engine suction
on the other.

The moving part comprises a hollow piston, which also

SCOTT-ROBINSON CARBURETTOR 211

acts as a dashpot, and contains within its interior a modu-
lating pin. This pin can be adjusted as regards vertical
direction by means of a screw and locknut in the head of
the piston. The fuel, issuing from the orifice under the
influence of engine suction, is precipitated within the
floating piston, and trickles out through a number of
small holes drilled round its lower edge.

This edge forms a valve seating, and is normally, when
out of action, located upon a conical portion of the
carburettor casing. The whole of the fuel thus passes
from inside the floating element, through the series of
holes, and meets the air stream passing through the
annulus round the outside of the floating element. An
even distribution of fuel in a fine spray is thus obtained,
and in this instrument the whole of the incoming air
passes in direct contact with the fuel.

The carburetted air passes directly upwards round
the casing of the dashpot and through a throttle of the
rotating drum type. As the demand of the engine
increases, the floating element rises, and is permitted
to do so by the dashpot, a small air-leak hole being
provided in the head of the floating piston to allow the
air in the dashpot to escape into the piston during this
process.

It will be noticed in this instrument that it is necessary
to do a certain amount of dismantling in order to make
the preliminary adjustments, as the floating element must
be removed for this purpose.

The modulating pin is, however, safely housed away
from all possibility of outside interference, and is not in
direct contact with any impurities which there may be in
the air stream. A small refinement will be noticed in the
method of fixing the lid of the float chamber, and one
which might be more generally adopted. This consists
of a number of metal balls, spring-actuated, which grip in
a groove in the float chamber lid, and allow the lid to be
removed without the use of tools.

212

CARBURATION

The " Scot " Carburettor embodies several unusual
features in its design, principally that of having eight jets
instead of the usual number.

In the illustration only two of these jets are shown, one "
of them being at A. All the eight choke tubes are formed

Fig. 57.— Scot.

in a sliding cone-shaped piece c, the mixture passages
B being continued upwards and passing into the mixing
chamber through the ports formed in the main tubular
body D of the carburettor. Within this body is an
automatic piston valve, which is shown separately in the
illustration, this valve being formed with slots of eight

SCOT CARBURETTOR 21 3

different lengths, and it is normally at the bottom of its
travel in the tubular casing D.

In this position one only of the slots is in line with a
port in the casing, and thus only one jet is operated upon.

It is claimed that this single jet is sufficient to run an
ordinary engine up to a speed of about 400 revs, per
min. when light, but as soon as a load comes upon it and
the throttle opens, the additional suction of the engine lifts
the automatic valve or piston so that the various slots in
turn come into operation, and so cause the fuel jets to be
acted upon. By this means the fuel and air supplies are
regulated automatically by the requirements of the engine
and the throttle movement.

The dashpot action for the piston is provided by
enclosing the space marked u so as to form an air
buffer and prevent a rapid downward descent of the piston,
and a small valve G is placed in the foot of this space so
as to admit air when the piston is required to lift. Thus
the air damper only acts in one direction, and it will be
noticed that the choke tubes are of taper section, and by
means of an adjustment, provided in the form of a knurled
nut F, the latter can be raised to any desired extent, so
that the effect of an adjustable choke tube is obtained for
each jet.

In this instrument passages are provided communicating
between the jet chamber and the float chamber, these being
formed within the cover of the float chamber and the walls
of the jet chamber, the effect being to equalise the pressure
between the two chambers. When the pressure in the
vicinity of the jet chamber is much lowered by the suction
of the engine, depression of pressure also occurs in the float
chamber, thus in a manner neutralising the tendency for
the jets to discharge an excess of fuel.

The " Senspray " Carburettor acts on an entirely
different principle to other instruments on the market. It
is common knowledge, that if a current of air is blown

214

CARBURATION

through a nozzle of a small bore held at right angles to
the mouth of another similar nozzle, whose lower end is
immersed in some liquid, the liquid is sucked up the jet and
projected forward in the form of a fine spray. The success-
ful application of the principle has hitherto been confined
to such articles as " scent sprays," " artists' fixing sprays,''
and to the instrument known among medical men as a

i9^H

Fig. 58. — Senspray.

" nebuliser," which is used for spraying the throat and nose
with certain liquids of a healing or disinfectant nature. It
is obvious that the principle lends itself particularly well
for the purpose of perfectly atomising petrol, or other fuel,
for internal combustion engines.

Reference to the sectional diagram of the instrument j|
will show how the principle has been adopted in practice.
It will be seen that with the air shutter in its lowest or

SENSPRAY CARBURETTOR 21$

closed position, and the throttle only slightly open, the
velocity of the air through the vaporiser is increased, and
this gives the strong pulling at slow engine speeds, which
is accomplished in some instruments by means of a pilot
(or small) jet, in a separate small choke tube, without the
attendant disadvantages of the liability of a very small jet
to become choked.

A small volume of air is drawn by the engine suction
through the vaporiser or spraying nozzle at a high rate of
speed, directly over the top of the petrol jet, which forcibly
draws the petrol out of the jet and sprays it into the mixing
chamber in the form of a fine mist. At the same time the
air necessary to form the explosive mixture is admitted
straight in at the back of the carburettor, and a perfectly
atomised firing charge is thus obtained.

The instrument is of the well-known " straight-through "
type, giving at full throttle a clear way through into the
engine, and is semi-automatic in action ; that is to say, that
except for starting, and to enable the engine to pick up
when it slows down on a severe gradient, the air lever can
be left open most of the time, and the driving done on
the throttle lever only.

The semi-automatic action of the carburettor is due to
the cylindrical rotary type of throttle valve used. It may
be termed a *' Duplex Valve," as, to a certain extent, it acts
in a two-fold manner both as an air and throttle valve.
Indeed, the use of this type of valve renders it an easy
matter to make the instrument entirely automatic, or one
lever-controlled, as having determined the largest jet that a
particular engine will take with full air and throttle, the
slot which is cut in the throttle to admit the air necessary
to complete the mixture at small throttle openings is then
opened out to give a good mixture at all points of the
throttle opening. The air valve can then be dispensed with ;
but the makers prefer not to do this, as even when it is
"tuned" to the engine in the way described above, it is
exceedingly difficult, if not impossible, to counteract the

2l6 ^^^^^ CARBURATION

variation in atmosphere, variations in the gravity of the
fuel used, and variations in engine speed (and hence suction
on the jet), at a given opening of the throttle due to the
varying gradients of the road. The makers believe that
these difficulties can only be met by the use of a separate
air control, which in the case of the Senspray is con-
veniently incorporated in the handle-bar control (for motor
cycles).

The throttle is supported in ample bearings at each
side, and as all air admitted to the instrument passes first
through a large gauze dust cap (which effectively excludes
all grit), there is no tendency for the valve to stick.

The air shutter works round the periphery of the
throttle valve, being pivoted on the throttle spindle-bearing,
and the return of both valves is secured in a very ingenious
manner by the action of one strong rust-proof clock-
spring.

The float chamber, which is adjustable at either side
of the instrument, follows the standard practice, and
although a " tickler " is fitted to the cap, there is in
practice no necessity for its use.

The jet is instantly accessible without disturbing any
other part of the instrument, and as the base (or jet
holder) is conical in shape, a sound metal to metal petrol-
tight joint is assured.

Solex. — The Solex (Fig. 59) is of French origin and
manufacture, of the two-jet type, but it differs very con-
siderably from other two-jet instruments which have
previously been dealt with. The most interesting feature
of the Solex is the arrangement of the slow running jet,
and the means provided for introducing the mixture to
the engine side of the throttle when this jet is in operation.
It will be noticed that the central tube in the float chamber
around which the float is situated is fitted at the top with
the slow running jet, and the petrol is drawn up this tube
through the hole near its base shown in the diagram.

SOLEX CARBURETTOR

217

Some of the air supply for slow running enters the small
ball valve at the top of the float chamber, the air passing
downwards and across the top of the supplementary jet.
The mixture then passes through the passage towards
the choke tube, and thence vertically upward through the
throttle trunnion, and to that part of the carburettor
situated between the two halves of the butterfly throttle
valve. In order to start up, therefore, the throttle must

Fig. 59. — Solex.

be put in its closed position. The object of the ball is to
reduce the suction over the smaller jet when the throttle is
nearly closed. The actual passage of the mixture for slow
running is regulated by means of moving the throttle
bodily in the direction of its axis, and the end of the
throttle where the mixture enters can be drawn sideways,
thus forming a valve. If the auxiliary jet is obviously on
the large side, the throttle can be adjusted laterally to
give the necessary amount of mixture, and then a smaller

2l8

CARBURATION

slow running jet can be fitted of such a size that the engine
will run slowly without missing fire. The larger the
auxiliary jet, the better will be the pick-up. In addition
to these two adjustments there are two more main adjust-
ments for power, these being the main jet and the choke
tube. There is thus in this carburettor ample scope for
anyone who is that way inclined to make numerous adjust-
ments. Fortunately, however, these adjustments, when
once made, are not easily capable of derangement, as they
are mostly of a fixed nature. The design for the carburettor
lends itself to easy dismantling, and the one large nut
situated above the float chamber holds the two main
portions of the instrument together. Furthermore, the
large washer beneath it holds in position both the petrol^BI
union and the tap over the ball valve. It will thus be™'
seen that when this nut is slacked back the carburettor
can be taken to pieces for adjustment, if the petrol needle
valve is held upon its seat by any convenient means.
This valve is normally pressed up to its seat directly by
the top of the float, and no toggles or levers are necessary.
The carburettor is not water-jacketed, and a hot-air supply
is recommended.

In the latest form of Solex a composite jet is fitted,
which allows a certain amount of air to pass through a
tortuous passage and mix with the issuing stream of fuel

Such an arrangement increases the
particularly at high engine speeds.

atomising effect,

Stewart Precision. — One of the latest successful
carburettors overcomes any difficulties of the adjustment
of petrol level, for in the Stewart " Precision " (Fig. 60)
this level is some 3 in. below the actual orifice through
which fuel issues to the mixing chamber.

The Stewart Precision carburettor is of the constant
suction type, and immediately a normal condition of
working is arrived at the difference of pressure is of the
order of 9 to 10 in. of water-head. The main working

STEWART PRECISION CARBURETTOR

219

element consists of a gun-metal valve supported in the
air stream, and provided with a small central tube dipping
at its lower end into the float chamber, its upper end being
level with the top of the valve.

For some distance along the upper length of this

Fk;. 60. — Stewart Precision.

tube is an annulus, communicating by means of a
number of holes with the lower or atmospheric side of
the valve.

The air passes through the valve and up the annulus,
drawing with it petrol through the centre tube.

The main hole through the valve head is f in. diameter,

220

CARBURATION

whilst the inside diameter of the petrol tube is |^ in., and
it terminates about |^ in. from the level of the top of the
valve.

This small tube extends downwards to a petrol well,
formed within the valve stem, and the valve stem itself
is provided with a lower extension tube | in. long, and
J in. diameter outside in the i:|-in. carburettor.

It is this lower extension which is used for regulating
the supply of petrol to the engine, and its method of opera-
tion is as follows : —

When the floating valve controlling the air and petrol
supply is on its seat, sufficient air passes through the valve
by way of the eight holes admitting air from below, and
through the valve head to the mixing chamber by way
of the central f-in. hole. This air is concentrated, therefore,
round the orifice of the central tube, thus enabling a
sufficiently high suction effect to be obtained when the
engine is cranked round by hand at starting.

Continuing the consideration of the ij-in. type, which
type, by the way, is most suitable for engines of the 3-litre
capacity, and supposing that the engine is properly tight,
the valve will remain upon its seat until a speed of 130
r.p.m. is reached, when the cylinders are 100 per cent, full
of mixture.

Naturally, when the throttle is closed and an attenuated
charge is admitted, the engine speed can be increased up
to somewhere about 200 r.p.m. or more, depending upon
throttle tightness and absence of leakage before the valve
commences to rise. ^^

The admission of petrol through the valve by means
of the lower projecting tube is controlled by a taper pin,
provided with a suitable adjustment passing through the
lower part of the float chamber.

When the valve is on its seat the taper pin is lowered,
so that the annulus round it permits of the correct flow of ^|
petrol to suit the amount of air passing at the minimum
slow running, and in slow running positions the increase of

11^

STHENOS CARBURETTOR 221

petrol flow is produced by the increased suction as more
air passes through the valve.

When the point of equilibrium is arrived at, the valve
commences to lift off its seat, and air passes round the
outside of it as well as through its centre.

From this point it is important that the rate of change
of area of the petrol annulus should be the same in
proportion as the rate of change of air annulus, making
due allowance for friction and viscosity in each case.

These rates of change depend upon the shapes of
the passages, and there is, of course, a constant and a
variable in both cases. In carrying out numerous experi-
ments with this instrument many important and interesting
points have come to light, and particularly the influence
of the shapes and sizes of the taper pins upon the resulting
petrol flow.

In the first place, it will be noted that the regulating
device is always submerged in petrol and is not, as in the
majority of other carburettors, an intermediary between
petrol on the one side and air on the other side. It does
not, therefore, function as a spraying device. We have,
however, to take into account the effect of hydraulic
friction, but not capillarity. As the suction is constant
at all speeds after the valve has commenced to lift, one
would expect to get a flow of liquid proportional in
magnitude to the area of the annulus, neglecting the
difference in the friction of the orifice between the limits
of working. This frictional effect is somewhat curious, for
one must bear in mind that when the annulus is small,
the ratio of the length of annulus to its net area is greater
than when the valve has lifted, and when a greater volume
per unit of time is passing.

Sthenos. — The Sthenos carburettor (Fig. 6i) is one
of the oldest carburettors in existence, and was in all prob-
ability the first instrument in which a Venturi choke tube
was used, the early type being fitted with a jet tube

222

CARBURATION

terminating in a mitre-seated valve, which could be adjustet
by means of a small screw passing down the centre of the
jet, fitted with a nut at its outer extremity. The modern
Sthenos carburettor naturally differs considerably from the
early type, its two principal points of divergence being
in the adoption of a double jet — the small one for slow
running only — and the use of a resistance screw in the fuel
passage to the main jet. First considering the pilot jet, a.

Fig. 6i

small orifice is fitted at the base of the fuel passage, which
at its upper end communicates with the throttle chamber at
the engine side of the throttle when the latter is in its closed
position. This petrol uptake is open to the atmosphere,
but a small internal fuel pipe is provided through which
the petrol can pass on its way to a second small orifice
which allows only sufficient fuel to pass through it to run
the engine slowly. A small air pipe is provided to admit

S.U. CARBURETTOR 223

sufficient air to the supplementary fuel orifice for slow
running, and this fuel and air supply become inoperative as
soon as the throttle is opened. Now, with regard to the
main supply, the resistance screw in the fuel passage has
already been referred to, and in a previous chapter it has
been pointed out that the shape of these screws could not
be calculated theoretically, but could only be arrived at
by practical methods. The presence of this screw in the
Sthenos carburettor is probably the only instance of the
continuance of this type of regulation in modern practice,
and no doubt the lengthy experience of the manufacturers
of this instrument has enabled them to produce a screw
which gives satisfactory results. The damping out of an
excessive fuel supply under high depression is also assisted
in the diminution of fuel head as the demand of the engine
increases. It will be noticed that the supplementary jet
is cut out of action altogether as soon as the fuel level
falls below the extremity of the small internal pipe which
supplies the supplementary jet. The modern Sthenos
carburettor has certain features of other well-known types
with regard to its adjustment, and it particularly calls to
mind the Zenith in several of these respects.

S.U. — Important amongst the constant suction types of
carburettors is the S.U. (Fig. 62), adopted extensively by
the VVolseley Company. This carburettor is of the modu-
lating pin type, but in distinction to the instrument already
described, the pin is exposed to the air flow, and its range
of working is much larger than that of the Stewart.

The main feature of the S.U. carburettor is the com-
bination of air choke with a variable jet orifice, and it is
so operated that the air stream is concentrated at right
angles to the fuel stream, the air velocity being always of
constant magnitude. The operation of the instrument is
by means of a single moving part comprising a piston,
fitted with a modulating pin, and working against the action
of gravity, tending to lower the piston, and the suction of

224

CARBURATION

the engine tending to raise it. As distinct from many
types of constant suction instruments, the S.U. moving
portion is set at an angle of 45° to the vertical, and
there are thus variable forces coming into play when the
instrument is set in a fore and aft position on a car. These
variations may be due to the position of a car at any time

Fig. 62.— S.U.

upon a hill, as the vertical component of the action of
gravity in a downward direction will vary in magnitude
with the angle of the instrument. For this reason the
Wolseley Company fit the S.U. carburettor transversely,
thus obviating one difficulty as long as the car remains on
a flat road, and does not heel over on one side or the other.
Piston tightness, and consequently friction of the moving

S.U. CARBURETTOR 225

part, is eliminated by the use of a leather bellows attached
to the operating piston at one end, and to the carburettor
casing at the other end, there being a communicating
passage between the interior of the bellows and the portion
of the mixing chamber on the air side of the throttle.

Thus the suction below the throttle at any time is
communicated to the operating piston, causing it to move
upwards until the normal intensity of suction is reached.
The air piston being directly connected to the throttle
piston causes the latter, together with the modulating pin,
to work in unison, and to open the air inlet in direct ratio
to piston linear movement, but the modulating pin can be
formed as desired to suit any particular engine.

We have already seen that with pins, having a uniform
taper, the flow of fuel is not exactly proportional to the
linear movement of the modulating pin. As a result of
experiment, therefore, the pin must be formed to give a
correct mixture of fuel to air at any position of the pin
and the air piston.

As distinct from some other types of constant suction
instruments, the S.U. is arranged so that the whole volume
of air used by the engine is carried across the fuel stream,
through what is virtually a choke tube of varying dimensions,
and it must be remembered that the air velocity through
this tube is constant at all times. In order to give sufficient
concentration and suitable shape for the air stream at low
demands, the surface surrounding the jet is formed into
a ridge with the jet let flush into it. The lower part of
the choking piston is also formed concave, so that, when
this piston is at its lowest position, an effective area or
constant leak of one-twentieth of a square inch is provided.
Referring to Fig. 62, one or two points will be evident
which call for some comment.

The method of adjustment for the pin leaves some-
thing to be desired, as, in order to raise or lower the position
of the modulating pin relatively to the choke piston, it is
necessary to open up the carburettor and release the small

226

CARBURATION

screw which holds the pin in position. This adjustment
cannot, therefore, be made whilst the engine is running.
It is only fair to state, however, that the pin adjustment H
is an extremely easy and rapid operation once it has been
removed from the carburettor, together with the bellows.
This carburettor requires a hot-water jacket, and, like other
constant suction instruments, difficulty may be experienced
when starting cold until the normal working temperature
has been reached. One might expect to find trouble in
connection with the leather air bellows, but apparently this
part of the instrument does not suffer from undue wear h
and tear in actual practice. "

A great point in favour of this carburettor is its small
and compact form, and the smallness of the obstruction f
which it offers to the air flow. For high efficiency work
it should, therefore, give very fine results. The throttle
employed is of the ordinary butterfly pattern.

The Stromberg Carburettor. — The Stromberg car-
burettor is made in several models, the " A " and " B "
type being of the single jet, while the " C " is a double jet
design — " B " being of the concentric float construction for
small engines, whilst " A " and " C " are of the usual
Stromberg pattern, with the float chamber at one side ;
the float chamber being made of a glass tube, which is one
of the distinctive features of the Stromberg carburettor.

Some of these instruments are water-jacketed around
the Venturi tube chamber, whilst other types are hot-air
heated.

The latest Stromberg two-jet carburettor has, in addition
to the main central jet, a subsidiary jet fitted slightly to
one side, in a horizontal passage between the mixing
chamber and the auxiliary air valve. This jet has an
adjustable needle valve regulation (not shown).

The auxiliary Venturi tube, which is now fitted over the
main jet, is threaded into the carburettor body. This part is
so grooved that an opening extends round the Venturi,

STROMBERG CARBURETTOR

227

The side of this opening towards the float chamber opens
through the main body of the carburettor to the atmos-
phere, and the other side opens in the fuel pipe leading
to the auxiliary nozzle at a point above the fuel level.
Its operation is as follows : The primary nozzle in the
Venturi supplies all the fuel necessary for slow speed
running, but as the motor speed increases the suction on

Fig. 63. — Stromberg (earlier type).

the auxiliary fuel nozzle also increases, but no fuel issues
from this nozzle until the suction of the motor becomes
greater than the capacity of the leakage hole connected
with the atmosphere to the groove around the Venturi.

After this point is reached the fuel flows through the
supplementary nozzle, its flow increasing or decreasing
with the motor's speed.

Model " B " is so arranged that the needle operating

228

CARBURATION

the auxiliary jet is controlled by the auxiliary air valve.
This valve, being a new design, works in a chamber
surrounded by a sleeve which can be operated from the
dash. This sleeve fixes the size of the air opening for the
valve, the hollow valve stem carrying two pistons operating
in a dashpot so as to control the quality of the mixture
issuing from the jet, depending whether the sleeve air^
opening is exposed to a lesser or greater extent.

Trier and Martin. — Probably one of the best known
multiple jet carburettors in this country was the T. and M.
(Fig. 64), the principle of which has already been alluded
to. This instrument is of the right-angled type, its main
features being the combination of three or more fuel
jets, with a suitably formed horizontal sliding sleeve
throttle, so arranged that the mixture openings vary with
the uncovering of one or more of the jets. By the use
of three jets in series, where the air stream passes across
the tops of the jets at right angles, there is of necessity
a certain irregularity of fuel operation which is far
more pronounced than in types such as the Polyrhoe,
where the number of jets is large. In the T. and M.
carburettor, however, this effect was reduced by forming
small wells round each jet, situated closely to one another,
so that the tube or sleeve which travels across the tops of
these wells spreads out, as it were, its blanking effect over
a larger area than it would do were it simply to pass across
the jet orifices.

The throttle sleeve, with its extension piece, being
hollow, allows the mixture of fuel and air to pass through
its centre, and form in reality a mixing chamber, the
intensity of the air stream being regulated by means of a
rotary air shutter situated at the inlet end of the instrument.
The main air supply to the choke tube is conical in form,
and is provided with a spring-closed valve in the centre
of the rotating air shutter, so that at high engine speeds
an additional supply of air is allowed to enter. With

TRtER AND MARtiN CARbURETtOk

229

regard to the jets, these are three in number in the small
sizes of carburettors, whilst in the larger sizes there may
be as many as four or five. Over the top of the jets is a
removable plate, through which they can be inspected or
withdrawn, and in the side of the jet chamber small holes
are drilled so as to allow a certain quantity of air to be
drawn directly through the jet pockets, thus creating a
fine spray of fuel. In order to obtain slow running, a by-
pass is provided, which draws air at a high velocity across

Fig. 64. — Trier and Martin.

the second jet when the throttle is closed, and the mixture
is delivered to the engine side of the throttle by means of
a small tube passing through the water jacket. This jacket
embraces the body of the carburettor round the air throttle
casing, and the slots in the air throttle are so shaped as to
give a gradual opening.

Vapour. — The vapour carburettor (Fig. 65) has recently
made its appearance. This particular instrument is so

:230 CARBURATION

arranged that the petrol well or tube over the jet com-
municates with a small hole passing out at the engine side
of the throttle, and another small air hole is provided so
that, in the initial stages of starting up, the petrol is drawn
from the well and up the small tube more or less in bulk.

Fk;. 65. — ^ Vapour.

As soon as the well is exhausted the jet is no longer
submerged, and a stream of air at high velocity issues with
the petrol from the small hole situated in the top of the
starting well, the air passing across the top of the petrol
jet and helping to spray the petrol up the tube and into

VAPOUR CARBURETTOR 23 1

the carburettor body. This instrument is provided with a
choke tube, and the two adjustments consist in the replace-
ment of this choke tube or of the jet as may be desired.

In arriving at the size of the various parts of this
carburettor the diameter of the choke tube is the basis
from which the calculations are made — or from which
experiments originate. It is the practice of the makers
to adopt the well-known formula based upon cylinder
diameter and compression ratio, which is as follows : —

II
where ^=the diameter of the choke tube.

D = the diameter of the cylinder in the same units.
R = the compression ratio.

This formula takes no account of stroke.

Ware. — The Ware carburettor (Fig. 66) is probably
best known in connection with the Straker-Squire car,
upon which it has appeared as a standard fitting for some
years past. Although its general appearance has altered
from time to time, its general principle has remained as
follows : The carburettor jet proper consists of a small
nozzle submerged in the fuel in the float chamber ; in the
earlier type this nozzle was situated at the end of a vertical
tube, provided with a central adjustment needle, terminating
at the top in a milled-headed screw. In the top of this
tube two holes were drilled, allowing a certain amount of
air to enter and pass down the tube, meeting the petrol as
the latter passed upwards to the engine. In order to
arrange this adjustment conveniently it was necessary for
the air stream to enter the carburettor horizontally, and
through a horizontal throttle. In the later arrangement
this conical horizontal throttle has been dispensed with,
and a more convenient form of plate throttle and choking
tube employed. It will be seen that the concentric petrol
and air tubes iiave been retained, but without the means
of adjustment ; this latter is eliminated by employing fixed

232

CARBURATION

orifices and a double system of operation. Supposing, now,
that the plate throttle is shut, there will be a considerable
depression at the engine side of the throttle, and the means

Fig. 66. — Ware.

WELSH CARBURETTOR 233

of air inlet will be down one of the vertical tubes and
upwards through the centre tube, carrying the petrol with
it. A maximum of suction will, therefore, be experienced
at the end of the central petrol nozzle. Now, when the
throttle is open and the engine demand is great, the point
of maximum depression in the system will be at the throat
of the choke tube. The action will, therefore, be as follows :
Air will enter the outer annulus between the two larger
vertical tubes, and will pass through the petrol by way of
the perforations in the second tube, and will issue, together
with a certain amount of petrol, up the annulus between the
second tube and the central tube. When the suction is a
maximum a certain amount of petrol will also pass up the
central tube, its flow being governed by the size of the jet
orifice at the lower extremity of that tube. There is thus
a combination of jet and surface carburation taking place,
and this combination can be adjusted to give very satis-
factory results under all conditions of working, and it may
be added that in practice quite an abnormal "pick-up" is
obtained with good fuel economy.

Welsh. — The Welsh carburettor (Fig. 6'j') is a form of
multi-jet instrument, having a downward air-flow through
two small vertical tubes situated in the float chamber.
These tubes are provided with a number of apertures
of various sizes in each, corresponding with a series of
figures stamped on their upper edge. The tubes are
lightly held in position, and can be rotated or moved
at will whilst the engine is running, so as to bring any
desired aperture into working position. In the base of the
instrument a rotary throttle is fixed, ahd divided into two
compartments ; the first portion of the throttle movement
communicates with one of the small tubes, and on opening
the throttle further the second tube is also brought into
operation. These inner tubes, by means of their perfora-
tions, communicate with the float chamber, and the down-
ward stream of air draws a certain quantity of fuel from

234

carburation

the float chamber in accordance with the velocity of air
passing and the size of the hole employed. This instrument
is simple and compact, but the holes through which the
fuel passes should be carefully made in order to ensure
satisfactory working. The stream of mixture issues in a
direction at right angles to the downward air-flow, and

Fig. 67.— Welsh.

the inlet of petrol to the float chamber is controlled hy a
long vertical needle and a lever with an adjustable fulcrum.
This adjustment is necessitated in order to maintain the
petrol level on a level with the apertures in the jet sleeve,
otherwise either flooding might occur or the instrument
might refuse to work on account of these apertures being
above the petrol level. This carburettor is not jacketed.

WHITE AND POPPE CARBURETTOR

235

White and Poppe. — The double adjustment is
simplified in carburettors of the White and Poppe type,
in which the jet consists of a fixed and rotating part, the
fuel holes being drilled eccentrically, so that when one part
rotates relatively to the other the effective aperture becomes
increased or diminished in size according to the degree of
rotation. In the White and Poppe carburettor a jet cap

Fig. 68. — White and Poppe.

is combined with a rotary throttle, which acts upon the
incoming air and the outgoing mixture simultaneously ;
such an arrangement being, so to speak, " mechanically
automatic."

The White and Poppe carburettor (Fig. 68), to which
brief references have been made from time to time with
regard to the means of varying the jet orifice, has other

236 CARBURATION

important features which will bear further discussion, f
has been found, for instance, as the result of numerous"
experiments, that the most suitable area of petrol orifice
for any particular carburettor is fixed definitely, and that
the ratio of area of the petrol orifice to that of the air
orifice is i to 500. It will thus be seen that when the two
holes in the jet which become concentric at full throttle
opening are of the same size, a definite relation exists at
all throttle positions between the air and petrol orifices.
However, if one of these holes be reamered out slightly
larger, a certain lead can be given to the petrol orifice,
the effect of which is similar to that obtained in other
instruments which have already been under discussion.

The latest type White and Poppe carburettor is fitted
with a constant air-leak over the top of the jet orifice, the
area of which can be fixed at any desired value. In place
of the plain hole of the earlier instruments, a cam-shaped
plate is fitted in the later models as a cover to the constant
air-leak hole, and this plate can be located in any of twelve
different positions, thus giving a wide range of adjustment.

The throttle of the White and Poppe is of the ordinary
barrel type, but it is of much larger dimensions than, for
instance, the throttle of the Claudel, which latter almost
completely surrounds the jet. As a result the jet chamber
in the White and Poppe is of a considerable capacity, and
in closing the throttle there is an absence of that concen-
tration of air-flow which is generally desirable for slow
running purposes.

There is, however, a certain amount of wire drawing of
the air stream on the inlet side to the throttle which is
silenced effectively by means of two corrugated strips of
copper, as wire drawing in the ordinary way produces an
objectionable noise when the engine is working.

Zenith. — Two-jet or multi-jet carburettors working
on varying suctions are examples of the diversion of the
air stream under no load or light load conditions of wor

ZENITH CARBURETTOR

237

ing. The Zenith (Fig. 69) is one of the most popular
of this type of instrument, and here we have a subsidiary
petrol duct fed from the float chamber at a constant rate
of flow by means of a suitable checking device. This
secondary supply rises up 'a. small tube opened to the
atmosphere at the top, and dipping into it is an internal

^^^i^^^^^-;|

^H^iOTZZSZ^'^

Fir,. 69. — Zenith Two-Jet Carburettor.

pipe carried up to a point in the vicinity of the throttle
valve. Although the suction due to slow running may
be insufficient to cause the petrol to flow through the main
jet, it will suffice for drawing enough liquid up to the
subsidiary tube, the point of discharge of which is situated
in a restricted part of the

gas outlet from the carburettor.

238

CARBURATION

In designing this carburettor the following essentials have
been borne in mind : that carburation should be unaffected
by the variation in the speed of the engine or of throttle

Fk5. 70.— The " M.P." Jet Arrangement for Zenith.

ZENITH CARBURETTOR 239

Opening, that the engine should pick up quickly and start
easily from cold, and that the carburettor should be devoid
of moving parts. With regard to speed variation and
throttle opening, any good design of carburettor should
be independent of these, but it is still a moot point as
to whether a moving part, if simply constructed and not
liable to suffer from wear, is a disadvantage or not.

Reverting to the curves of petrol flow previously referred
to, it will be remembered that in apparatus of this kind,
where the difference of pressure between that of the atmos-
phere and that in the vicinity of the jet varies throughout
the working range, the flow of petrol does not vary in
direct proportion. In the Zenith carburettor the com-
pensating jet is introduced in order to give a flow of
petrol in inverse ratio to that of the main jet. If the
design is correct in any particular case, the result should
be a straight line curve for the petrol flow. The duplex
jets of the Zenith carburettor are arranged concentrically,
and their levels coincide, the central jet communicating
with the float chamber, while the external jet communicates
with the small tube into which the starting tube also dips.
The flow of fuel to the external jet is controlled by a
choking plug, the size of which can be arrived at by trial
and error. This carburettor is supplied with a Venturi tube,
situated in the vicinity of the jet, and so there are three
variables capable of adjustment, as follows : —

a. The main jet.

b. The choking plug controlling the external jet.

c. The Venturi tube.

The Zenith carburettor, like the White and Poppe,
depends for its heat supply upon the necessary heat being
added to the incoming air, as there is no jacket to the
carburettor itself. The principle of this carburettor is based
on Rummel's formula, given on p. 61.

Jets. — The new and modified means of adjusting the
low load or starting jet, lately adopted by the Zenith

240

CARBURATION

Carburettor Company, will be readily grasped by reason
of its extreme simplicity.

The well above the compensator, in this new system,
does not as usual hold the tube through which the petrol
for slow running passes, but this tube is screwed inside
another tube M, with a petrol inlet E of definite size drilled
in the bottom of it, and an air hole A, also of definite size,
at the side of the tube near the top.

The part B has two passages drilled at right angles
to one another, with a milled knob which makes a push-fit
in the well j. These passages coincide with the outlet U
in the mixing chamber, which is situated just behind the
edge of the butterfly throttle when closed. A pipe P,
bevelled at the bottom, is fixed in the vertical hole in
piece B, and dips down into the petrol in the intermediate
tube M. This intermediate tube M is fed by the com-
pensator I, and is placed in the well j.

The suction at the petrol inlet E, and the flow of air
into the tube M, are both controlled by means of the hole
A drilled in this tube.

The sizes of the holes A and E in the tube M are
entirely independent of the size of choke tube, main jet,
and compensator, and are the only things to be considered
in adjusting this slow running device. Neither the length
of the dip pipe P nor the tube M affects the adjustment,
which is carried out after the ordinary tubing has been
done.

IB^

APPENDIX I

I calorie (major)
I B.Th.U.

Table LVI. — Equivalents.

- =3.968 B.Th.U.
= 0.252 calorie.

ERRATUM

Appendix I. Table LVI — Equivalents

For "i calorie per kilog. = 3.967 B.Th.U." read "i calorie
3.967 B.Th.U."

[ To face page 240.

I gal.

I cub. ft. -

I inch of water gauge
I American gal. -
I Imperial gal. -
I Imperial gal. -
I American gal.
I litre

= 4.546 cu. cms. = 0.1606 cub. ft.

= 28.3 litres.

= 6.28 gals.

= 25.4 mm. water gauge.

= 0.832 imperial gal.

= 1.2012 American gal.

= 4.546 litres.

= 3.784 litres.

= 0.2622 American gal.

240

CARBURATION

Carburettor Company, will be readily grasped by reason
of its extreme simplicity.

The part B has two passages drilled at right angles
to one another, with a milled knob which makes a nnc;h.fit

APPENDIX I

Table LVI. — Equivalents.

I calorie (major)

- =3.968 B.Th.U.

I B.Th.U.

= 0.252 calorie.

i" C. - - -

- =rF.

r F. - - .

_ 6° r*

I kilog.

- =2.204 lbs.

I lb. - - -

- =0.453 kilog.

I B.Th.U. per cub. ft.

- = 9 calories per cubic metre approx.

pr _ . . .

r = 32.2 ft. per sec. per sec.
\ = 981 cm. per sec. per sec.

TT^ per ' C.

- = :j-Jy per ° Fahr.

I kilog. per sq. cm. -

= 14.2 lbs. per sq. in.

I lb. per sq. in.

= 0.0703 kilog. per sq. cm.

I metre kilog. -

- ' =7.231 ft. lbs.

I ft. lb. - - -

= 0.138 metre kilog.

I metre

- =39-37 in. = 3.281 ft.

I ft. -

= 0.3048 metre.

I cub. metre

- =35-31 cub. ft.

I litre

= 0.22 imperial gal. = 0.03531 cub. ft

I calorie per kilog.

- =3.967 B.Th.U. per lb.

I gal.

= 4.546 cu. cms. = 0. 1606 cub. ft.

I cub. ft. -

r = 28.3 litres.
' I =6.28 gals.

I inch of water gauge

= 25.4 mm. water gauge.

I American gal. -

= 0.832 imperial gal.

I Imperial gal. -

= 1.2012 American gal.

I Imperial gal. -

= 4.546 litres.

I American gal.

= 3.784 litres.

I litre

= 0.2622 American gal.

242

CARBURATION

Table LVII. — Conversion from Degrees Baum6
TO Specific Gravity.

Degrees

Specific

Degrees

Specific

Degrees

Specific

Baume.

Gravity.

Baume.

Gravity.

Baume.

Gravity.

1. 000

0-853

0.753

0.986

0.843

0.744

0.972

0.833

0.737

0-959

0.823

0.729

0.946

0.814

0.721

0-933

0.804

0.714

0.921

0.795

0.707

0.909

0.786

0.700

0.897

0.777

0.683

0.886

0.769

0.666

0.875

0.761

0.651

0.844

APPENDIX II

NOTES FROM A PAPER BY Mr G. H. BAILLIE

The minimum temperature at which it is possible for a
fuel to exist as vapour under normal atmospheric pressure
is obtained from the vapour-tension curve of the fuel, which
is a curve giving the minimum temperature at which
the vapour has a certain pressure. The pressure of the
vapour in the mixture depends on the proportions of the
mixture, and can be calculated from the equation : —

■^ I + v6 '

APPENDIX II

243

where/ is the pressure of the vapour, V is the volume of
air in cubic metres which is mixed with i kg. of fuel, and 8
is the density of the vapour of the fuel at normal tempera-
ture and pressure. From this equation and from the
vapour-tension curves can be found the minimum tempera-
ture at which different pure fuels can exist as vapour. It
has been found that the best results are obtained in an
engine when the mixture contains about 30 per cent, more
air than the quantity theoretically sufficient to completely
burn the fuel. The results for four mixtures are given in
Table LIX.

Table LIX. — Minimum Temperature at which Fuel can

Exist as Vapour.

Air.

20 Per

Right

20 Per

40 Per

Cent. Less.

Amount.

Cent. More.

Hexane

-14.2

-17.7

— 20.6

- 24.2

Heptane

7-3

3-6

0.7

2.0

Octane

22.9

19.0

16.0

13.0

Decane

46.1

42.0

39-0

36.5

Benzene

-0.7

-4.3

-6.9

-8.3

Ethyl alcohol

26.5

23-3

20.7

17.8

From the above table it appears that octane, decane,
and alcohol cannot exist as vapour under ordinary atmos-
pheric conditions except in very weak mixtures. The
large difference between benzene and alcohol accounts
for some of the difficulty in using the latter as compared
with the former in an engine.

If these fuels were mixed with the air in the form of
liquid at these temperatures they would not vaporise
completely, for in evaporating they reduce the temperature,
and the fall in temperature due to evaporation, calculated
from the latent heats of the fuel and the specific heat of
the air, is shown in Table LX.

244 ■^^■" CARBURATION

Table LX. — Drop in Temperature Due to Evaporation'

Air.

20 Per

Right

20 Per

40 Per

Cent. Less.

Amount.

Cent. More.

Hexane

233

19.0

16.3

14.2

Heptane

22.4

17.9

15.0

12.8

Octane

21-5

17.2

14-3

12.3

Decane

18.5

14.8

12.4

10.6

Benzene

47.3

32.2

23-5

20.9

Ethyl alcohol

95-5

76.3

63-7

54.6

Alcohol lowers the temperature in evaporating twice
as much as benzene does, and benzene, according to Table
LIX., can vaporise at about the same temperature as heptane.

If the figures in Tables LIX. and LX. be added
together, the result gives the minimum temperature of the
air necessary to evaporate the fuel completely. This is
shown in Table LXI.

Table LXI.— Minimum Temperature of Air before

Evaporation.

Air.

20 Per

Right

20 Per

40 Per

Cent. Less.

Amount.

Cent. More.

Hexane

9.1

1-3

-4-3

- lO.O

Heptane

29.7

21.5

15-7

10.8

Octane

44.4

36.2

3^-3

25-3

Decane

64.6

56.8

51-4

47.1

Benzene

46.6

27.9

16.6

12.6

Ethyl alcohol

122.0

99.6

84.4

72.4

None of the fuels above mentioned, hexane excepted,
can be evaporated completely in a cold engine, whilst for
complete evaporation alcohol requires the air to be at the
boiling point of water. With 20 per cent, more air, heptane
and hexane can be vaporised cold. It is a noteworthy fact
that the temperature required for benzene falls very rapidly
as the mixture becomes weaker.

APPENDIX II

245

An important factor in the question is the rate of
evaporation. The time available is not nearly enough to
evaporate the fuels at the minimum temperature, and the
evaporation of liquid gets slower and slower as the space
into which it evaporates becomes filled with vapour.

August's approximate law states that the time required

for evaporation is proportional to log , where P is the

maximum and / is the actual vapour pressure at the
temperature in question.

The effect of the time required for evaporation can be
estimated only by calculating from this expression the
different temperatures which will cause the fuels to
evaporate in the same time, and by assuming for one fuel,
say hexane, that a certain increase of temperature above
the minimum is required to evaporate it sufficiently fast,
making the assumption that for hexane in a theoretically
correct mixture the air should be at the normal temperature
of 15° C, that is, that 13.7° must be added to the minimum
temperature in order to evaporate the fuel quickly enough.
On this basis, the calculations giving the additional
temperatures to be added in the case of the other fuels, to
produce evaporation in the same time, give values which,
used in conjunction with the previous table, produce
Table LXII.

Table LXII. — Temperatures before Evaporation to Cause
Evaporation in the Same Time for Each Fuel.

Air

20 Per

Right

20 Per

40 Per

Cent. Less.

Amount.

Cent. More.

Hexane

26.8

15.0

6.6

-0.8

Heptane

71.4

58.4

48.7

40.2

Octane

104.6

91.4

81.0

72.4

Decane

1493

136.0

126.4

118.4

Benzene

81.0

57.3

42.3

38.4

Ethyl alcohol

181.9

154.3

135-4

120.3

246

CARBURATION

The proportion of these temperatures which represents
the time element is certainly somewhat arbitrary, but the
figures represent as closely as is possible on theoretical
grounds the temperatures which would render the different
fuels equally volatile under running conditions of a
motor car.

Benzene has a higher boiling point than alcohol, and,
as shown in Table LXL, it is far more volatile than alcohol
under engine conditions, and for this reason it may be
concluded that the calculations leading up to Table LXL
give a better idea of the volatility than do the boiling
points, but it must be remembered that these calculations
are applicable only to pure substances and not to our
actual fuels, which are mixtures.

A mixture of two hydrocarbons in a certain proportion
gives off vapour which also contains the two hydrocarbons
in a certain definite but different proportion, there being
more of the lighter constituents in the vapour than in the
liquid, and the presence of the lighter constituents enables
the heavier to evaporate more readily than they would
alone. A petrol, then, evaporates as a whole, heavier
constituents evaporating more slowly than the lighter, but
more quickly than would be the case were they not mixed.
It is, therefore, impossible to calculate the volatility of
these complex mixtures, even if all the constituents are
known, and it can only be found experimentally.

INDEX

Acceleration, Newton's second

law of motion, 36
Acetylene —

effect on liquid fuels, 124
explosive limits of, 25
properties of. Appendix I
Ackermann, Mr A.S.E., A.M.I. C.E.,
"modulating" pin and its
functions, 49
Air —

inlet pipe pulsations, 39-44
properties of, 37 ; Appendix I
required for combustion, 23
saturation of by a vapour, 2, 14-

^9 . '
weight passing through an orifice,

47
Alcohol —

combustion limit, 21

explosion limits, 25

flow through small orifice, Sorel's

figures, 53
vaporisation and evaporation,
Baillie's figures, etc., 10,
19 ; Appendix II
American and European practice
in carburettor design com-
pared, 43, 106, 108
Annulus, see jets and jet orifices
Appendix I. — Properties of gases
Appendix 1 1. — Fuel tests, notes from
paper by Mr G. H. Baillie
August's law for evaporation of
liquid fuels ; Appendix II

Bailey-Dale carburettor, 151- 154

Baillie, Mr G, H., vaporisation

and evaporation of liquid

fuels, notes for paper.

Appendix II

temperatures of stability, 19

Ballantyne, Mr Horatio —

exhaust gas samples, examina-
tion of, 143
treatment of oil for motor
spirit, 124, 125
Barrel throttle, 113
Benzol —
calorific value, M. Edmund

Ledoux's figures, 130
combustion, Sorel's experiments,

etc., 21, 22
explosion limits, 25
flow through small orifice, author's
tests, etc., 54, 131, 132
Sorel's figures, 53
nitration, test for, 125
production, properties, etc., 128-

132 ; Appendix I
vaporisation and evaporation,
10, 12, 13, 19; Appendix
II
viscosity, Watson's table, 34
Binks carburettor, 164-156
Brewer carburettor —
description, 156-164
die casting, design for, 162
differential movement, 162
floating type, 162, 163
illustrations, 88, 159, 160, 163,

164
jet diagram, etc., 88, 160
limits of working, 156
mixed fuel tests, 126, 127,

128
moving parts, 107
S.U., adjustment for use with,

164
straight line movement, 162-

164
See also jets and jet orifices.
Brewer orifice

247

248

INDEX

Brown & Barlow carburettor, 155-
167
bicycle type, 166
pin operated type, 165

Butterfly throttle, 114

Carburation, definition of word,

132
Circular orifices, see jets and jet

orifices
Claudel-Hobson carburettor-
jet and jet orifices, fuel dis-
charge, etc., 100, 167, 168
coefficient of discharge, 61
effect of temperature upon
rate of flow, author's tests,
50-52, 54
features of jet illustrations,

etc., 100-102, 167, 168
graphical illustration of char-
acteristic discharge, 59
racing jet, loi

relations between area, pres-
sure, and discharge, practi-
cal data, 56-58
testing apparatus, 56, 58
suctions, discharge under

various suctions, 59, 60
See also jets and jet orifices,
circular orifices
mixed fuel tests at Brooklands,

126-128
racing model, loi, 169, 170
throttle, 113
Clerk, Dr Uugald, on exhaust gas

analyses, 141, 142
Constant suction carburettors,
features, etc., 5, 8, 156
Cfor particular instruments,
see their names)
Commercial spirit —
Anglo, 760
Borneo —
combustion of, 21, 24
distillation of, 12
flow through small orifices, 54,

specific gravity at different
temperatures, 51
author's tests of, 35

Commercial spirit {co?ttmued) —
Borneo {conii?iued) — ^'

viscosity and temperature,
effects of, 33-35» 5°
compared with benzol, 131
Watson's table, 34
Coquillon's combustion of methane
theory, 21 i

Daimler engine, Prof. B. Hopkin- ;
son's experiments upon ex-
haust gas analyses, 145,146
Dalton's theory of evaporation, 14
De Dion carburettor, 171 j

Decane — 1

properties of, 1 1 ]

vaporisatton and evaporation, 11,
10^ Appendix II
Definition^of letjTis used —
carburation, i
depression at the orifice or head

over the orifice, 2
homogeneity, i
inches of water-head, 49
modulating pin, 49
stratification, 2
units adopted, 48
Delaunay Bellevillecarburettor, 1 7™

.174

Depression at the orifice, defini-
tion, 2

Development of carburettor design,
4-6

Diesel engine, fuel consumption
compared with petrol en-
gine, 139, 140

Ease of starting in carburettors, 9
Eitner, explosive limits of mixtures.

Evaporation of liquid fuels, see

liquid fuels
Everest carburettor, 176-178
Excelsior carburettor, 174-176
Exhaust gas analyses, 141-149

Ballantyne's, Mr H., method,

143

Clark's, Dr Dugald, experi-
ments, 141, 142

Hopkinson's, Prof. B., experi-
ments, 145, 146

INDEX

249

Exhaust gas analyses {continued) —
limit caburettor, bench tests,

148, 149
Watson's, Dr,thermalandcom-
bustion efficiencytests, 147

Facile carburettor, 178-180
Float chambers —
action of float, 117
air vent hole, elimination of, 118
cork floats, construction of, 119
design, 116
difficulties of eliminating float

chambers, 116
fuel level, deviation from true

level, 117
fuel pipe, attachment of, 122
metal floats, construction of, 118,

119
methods of operating float valves,

117
needle valve area, 116
position relative to mixing cham-
ber, 121
Floating valves, see moving parts in

carburettors
Formulae, see useful formulae
Fuels, see liquid fuels

G. & A. carburettor, 180-182
G. C. vaporiser, 136, 138-146

consumption, maintenance, ex-
penses, etc., 139
Gases —
exhaust gas analyses, see that

title
liquid fuel, treatment by gases,

124
properties of. Appendix I
General principles of carburation,

Gillet-Lehmann carburation device,

5, 118

Heptane —
combustion, 24
properties of, 1 1

vaporisation and evaporation,
II, 19 ; Appendix II

Hexane —
combustion, 16, 26
distillation, 1 1
latent heat, 10, 29, 30
properties, 1 1
vaporisation and evaporation, 13,

18, 19 ; Appendix II
viscosity, 16, 24, 34
Holley carburettor, 106, 182-184
jet, 104

test on Reo car, 183
Homogeneous gases, 17, 20, 26-29

definition of homogeneity, i
Hopkinson, Prof. B., exhaust gas
analyses experiments, 145,
146
Hydrocarbons —
combustion of, 20, 27
petroleum series of, 10, 1 1
treatment for production of spirit,

123
vaporisation of. Appendix II
Hydrogen —

explosive limits, 25
properties of. Appendix I

Ideal carburettor, 184-188
Inches of water-head, definition, 49
Inertia, see inlet pipes and moving

parts
Inlet pipes and inertia, 36-47

American v. European practice

in inlet pipe design, 43
definition of word " inertia," 36
dimensions of orifices, effect on

the flow, 38
lonides', Mr A. G., theory, 38-

Newton's second law of motion,

pressure, Dr Watson s experi-
ments, 45-47
pulsations and turbulence, 38-

ratio of fuel to air, properties
of air, etc., 37, 38
lonides, Mr A. G., inertia theory,
38-41

J AVAL jet, 103, 104

250

INDEX

Jets and jet orifices, flow of fuel
through —
Annulus, fuel discharge, etc. —

coefficient of discharge, 74, 75

consumption tests with stan-
dard instruments, 78-80

graphical representation, 76, 'j']

importance of modulating pin
designs, tests with various
sized pins, etc., 73-82
Brewer orifice, fuel discharge,
etc. —

characteristic features, 83-86,
156

coefficient of discharge, 84,
88-90, 97, 160, 161

concentration of air-flow round
jet, 86, 156, 161

equations for discharge, 94-97

flutes, area of, calculations, etc.,
88, 91, 92, 94, 98, 99, 161

graphical illustrations of dis-
charge, 89, 91, 98

illustration of jet, 88, 160

modulating pin, adjustment,
etc., 83-85, 88

tables of discharge, 90, 91, 93,

.94,95,96,97,98

various combinations for re-
quired discharge, 97

vapour pressure, effect upon
discharge, 86-88

Sec also Brewer carburettor
Capillarity in jet orifices, 41
Circular orifices, fuel discharge,
etc. —

apparatus for measurement of
flow, 58

author's experiments with
Claudel carburettor, 54-60

coefficient of discharge, 61, 69,
72

errors and their effects, 63

flow of mixture through various
choke tubes, 66, 67

formulai for discharge, 61

equations for flow curves, 63,
64, 70, 72

graphical representation, 59, 62

limit quantity, flow under vari-
ous conditions, 64, 65, 70

Jets and jet orifices {continued') —
Circular orifices {continued) —

location of working range on
flow curves, 62, 63, 68, 69

measurement of surface ten-
sion, 61

Morgan's, Prof., experiments,
66, 67

multi-jet instruments, 69, 212,
229

pressure and discharge, rela-
tions between, 55, 57, 60,
62, 64, 66, 67, 69-72

regulation of fuel supply, 68
early types of jet carburettors,

4,5

functions and designs of car-
burettor jet, 54, 56

head over the orifice, or depres-
sion at the orifice, 2, 8

modulating pin, importance of, 8,

9, 11, 1 10
ruling factors in determining fuel

flow, 49
side orifices, 105
Sorel's experiments, 52, 53
special jets, 100-105
units of measurement, 48.

particular jets, see

titles.)

(For
their

Kerosene, see paraffin
Kingston carburettor, 188
Kreb's carburettor, early type, 5

Ledoux, M. Edmund, calorific

value of benzol, 130
Limit carburettor, 189- 191
bench tests, 148, 149
Liquid fuels —
capillarity, 41

carburation of air by means
132-140
forms of, 2
combustion, theoretical mix-
tures, Eitner's figures, 25
experiments with various

fuels, 24, 25
heat required, 29, 32
homogeneity, 26-29

INDEX

251

Liquid fuels {continued) —
combustion {continued) —
quantity of air required for,

23
surface to volume ratio for,
27-29
Commercial spirit —
composition of petroleum pro-
ducts, 13
distillation of spirits, 11, 12
evaporation, heat required,
G.C, vaporiser, 136-140
latent heat of, 6, 10, 14, 29
flow through circular orifices,

33, 34, 48-72

other forms of orifices, 74-

99
effect of temperature on, 5 1
inertia effects, 7, 45
lonides' theory, 38-41
homogeneity of mixture, see

combustion
mixed fuels, author's tests, 126-

128
petrol substitutes, j^^ petroleum

spirit
properties of, 11, 14, 19, 23, 29,

33
selective evaporation, 17
specific gravities at different

temperatures, 51, 52
temperatures of stability, 19
treatment of, detection by an-
alysis, 125
vaporisation of, 10-19 ; Appen-
dix II, 148
vapour pressure curves, 87
viscosity at different tempera-
tures, 33, 50
Watson's, Dr, tests, 34
weight of spirit compared with
air, 37
Locomobile jet, 105
Longuemare carburettor, 192
early type, 4

Mayer carburettor, 193-195

Methane —
combustion of, 21
explosive limits of, 25
properties of, Appendix I

Metric weights and measures table,
241

Mill's jet, 103

Modern requirements in carburet-
tors, 9

Modulating pins, 8, 9, 49, 73, 83-
85, 88, no

Morgan, Prof., experiments, 138
flow through circular orifices, 66,
67

Morris paraffin carburettor system,
140

Moving parts in carburettors, 106-

115

American and European prac-
tice, 106

dashpots, design and action of,
no, 113

effect upon explosive mixture,
no

floating valves, 107-no

effect of, upon depression in

mixing chamber, 108
spring action upon, 109, 112

inertia effect of, 7, ni-n3

modulating pin, see that title

spring controlled air valves,
68, 99, 106-109

throttles, n3-n5
Multi-jet carburettors, 236

Napier carburettor, 195-197
New Miller carburettor, 197
Newton's second law of motion, 36
Nonane—

combustion of, 34

distillation of, 1 1

properties of, 1 1

temperature of stability (Baillie),
19

Octane —

combustion of, 24

distillation of, 1 1

properties of, 1 1

temperature of stability, 19

vaporisation of. Appendix II
Orifices, see jets and jet orifices
Oxygen, properties of, Appendix
II

252

INDEX

Paraffin, carburation of, 132-140
G.C. system, 136-140
Morris system, 140
Standard system, 140
Diesel and petrol engine com-
parisons, 139, 140
difificulties in using, 135
flow through small orifices, 54
Morgan, Prof., experiments, 138
properties of, 13
vaporisation experiments, 12, 13,

Petrol engine, consumption com-
pared with Diesel, 139
Petroleum spirit —
combustion of —
air required, 23
calculation, 23
heat required, 29
experiments, 21, 22
constituents of, 2, 13, 22, 23
consumption in Daimler

engine, 145, 146
explosive limits of, 24, 25
flow through an annulus, 76-81
Brewer orifice, 93, 96
circular orifice, 56, 61, 62-70
long tube, 34, 52, 53
viscosity and temperature
table, 50
latent heat of evaporation, 6
properties of, 10-13, 19 ; Ap-
pendix II
substitutes for, 123-140
viscosity and temperature

effects, 33, 50
weight of, compared with air,

See also liquid fuels
Planhard carburettor, 199-201
Polyrhoe carburettor, 201, 204

dashpot. III

fuel flow, lonides' theory, 38-41

Rayfield carburettor, 204-206

Redwood, Sir Boverton —
combustion limits, 24
vapour saturation figures, 17

Rover carburettor, 168

Rummel's formula for jet discharge,
61

S.U. carburettor, 223, 226

Brewer's patent adjustment
164
Schebler carburettor, 206, 209 ^^h
Scot carburettor, 212 '^|

Scott- Robinson carburettor, 209-2 11

dashpot of, no -^^

Scott Snell, E.— !■

constituents of petroleum spirii^^

23
evaporation theory, 14, 15
Selective evaporation, 7-efer

liquid fuels
Senspray carburettor, 213-216
Sleeve throttles, 114
Solex carburettor, 216-218

jet, 102
Sorel's data —

combustion limits, 21, 22
evaporation of fuels, 11, 13, 18
flow of fuel through small

orifices, 52
viscosity and temperature
effects, 33, 34
Specific gravity of liquid fuels
conversion from degrees Baum^,^

242
See also liquid fuels
Spring controlled air valves, 68, 99,

106-109
Standard paraffin carburettor, 140^
Starting difficulties, 31
Stewart precision carburettor, 218-
221
dashpot of, III
inertia of moving part, 7
Sthenos carburettor, 221-223

jet, 105
Stromberg carburettor, 226-228

Terms used, see title. Definitions oC

terms used
Throttles, design of, 113-115
Trier and Martin carburettor, 228

Unwin, Prof., formula for co

efficient of discharge, 61
Useful formulie —
equivalent of metric units, 241
exhaust gas analyses, Ballan-
tyne, 125, 143

INDEX

-253

Useful formulae {continued) —
petrol flow through Brewer

orifice, 93-96
Rummel's, for rate of fuel flow, 61
vapour pressure, 14, 18 ; Appen-
dix II
weight of air through circular
opening, 47

Valve throttle, 1 1 5

Valves, floating, see moving parts

Vaporisation of liquid fuels, see

liquid fuels
Vapour carburettor, 229-231

formula adopted, 231
Viscosity of fuels, see liquid fuels

Ware carburettor, 231-233
Watson, Dr —

combustion and thermal effici-
ency, 22, 146

pressure in induction pipes, 45-

47
Weights and measures, units

adopted, 48, 241
Welsh carburettor, 233
White and Poppe carburettor, 235

Zenith carburettor, 236-240
de Dion type, 171
modified jet, 238
orifice design, 61

Printed at The Dakien Press, Edinburgh.

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CIVIL, MECHANICAL, ELECTRICAL &- MARINE ENGINEERING, 7

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CIVIL, MECHANICAL, ELECTRICAL ^ MARINE ENGINEERING. 9

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lo CROSBY LOCK WOOD &- SON'S CATALOGUE.

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12 C2WSBY LOCK WOOD &- SON'S CATALOGUE.

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CJVIL, MECHANICAL, ELECTRICAL ^ MARINE ENGINEERING. 13

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GAS LIGHTING FOR COUNTRY HOUSES. See Petrol
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14 CROSBY LOCKWOOD d- SON'S CATALOGUE

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CIVIL, MECHANICAL, ELECTRICAL «Sr» MARINE ENGINEERING. 17

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22 CROSBY LOCKWOOD &> SON'S CATALOGUE.

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CIVIL, MECHANICAL, ELECTRICAL ^ MARINE ENGINEERING. 23

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24 CROSBY LOCKWOOD &- SON'S CATALOGUE.

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CIVIL, MECHANICAL.ELECTRICAL 6- MARINE ENGINEERING. 25

STEAM ENGINE. A Text-Book on the Steam Engine, with a
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STRAINS, HANDY BOOK FOR THE CALCULATION

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SUPERHEATED STEAM, THE APPLICATION OF, TO

LOCOMOTIVES, See Steam.

26 CROSBY LOCKWOOD 6- SON'S CATALOGUE.

SURVEYING AS PRACTISED BY CIVIL ENGINEERS

AND SURVEYORS. Including the Setting-out of Works for Construc-
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SURVEYING SHEETS FOR PROFESSIONAL AND

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SURVEYING, LAND AND ENGINEERING. For Students

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SURVEYING, LAND AND MARINE* In Reference to the
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SURVEYING, LAND AND MINING, As applied to

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SURVEYING, PRACTICAL. A Text-book for Students Pre-
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SURVEYING, TRIGONOMETRICAL* An Outline of the

Method of Conducting a Trigonometrical Survey. For the Formation of
Geographical and Topographical Maps and Plans, Military Recon-
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SURVEYING WITH THE TACHEOMETER. A Practical

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CIVIL, MECHANICAL, ELECTRICAL &- MARINE ENGINEERING. 27

SURVEY PRACTICE, For Reference in Surveying, Levelling,
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With Tables, Illustrations, and Records. By L. D'A. JACKSON,
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SURVEYOR'S FIELD BOOK FOR ENGINEERS AND

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and Set Square only ; Levelling with the Theodolite, Setting-out Curves
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TECHNICAL TERMS, ENGLISH^FRENCH, FRENCH^

ENGLISH: A Pocket Glossary ; with Tables suitable for the Archi-
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TECHNICAL TERMS, ENGLISH^ GERMAN, GERMAN-

ENGLISH: A Pocket Glossary suitable for the Engineering, Manu-
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316 pp. Waistcoat-pocket size, limp leather. ... ... N'et 2S. 6d.

TELEPHONES: THEIR CONSTRUCTION, INSTAL^

LATION, WIRING, OPERATION AND MAINTENANCE. A
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TELEPHONES: FIELD TELEPHONES FOR ARMY

USE : INCLUDING AN ELEMENTARY COURSE IN ELECTRI-
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TELEPHONY: A COMPREHENSIVE AND DETAILED

EXPOSITION OF THE THEORY AND PRACTICE OF THE
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*»* Graphic in its treatment, this work is easy to understand, and will add to the knowledge of
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types of telephone systems.

TELEPHONY* See also Wireless Telephony and Wireless
Telegraphy.

28 CROSBY LOCK WOOD &= SON'S CATALOGUE.

THREE PHASE TRANSMISSION* See Electrical Trans-
mission OF Energy.

TOOLS FOR ENGINEERS AND WOODWORKERS.

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65.

TRAMWAYS: THEIR CONSTRUCTION AND WORK-

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TRUSSES OF WOOD AND IRON* Practical Applications
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TUNNELLING, PRACTICAL. Explaining in detail Setting-out
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CIVIL, MECHANICAL, ELECTRICAL &> MARINE ENGINEERING. 29

WATER, POWER 0¥. As Applied to Drive Flour Mills and to
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Glynn, F.R.S., etc. New Edition. Illustrated. Crown 8vo, cloth 2s.

WATER SUPPLY OF CITIES AND TOWNS. By

William Humber, A.M.Inst.C.E. and M. Inst. M.E., Author of " Cast
and Wrought Iron Bridge Construction," etc., etc. Illustrated with 50
Double Plates, i Single Plate, Coloured Frontispiece, and upwards of
250 Woodcuts, and containing 400 pp. of Text. Imperial 4to, elegantly
and substantially half-bound in morocco ... ... ... Net £6 6s.

LIST OF CONTENTS : — I. Historical Sketch of some of the Means that have

BEEN ADOPTED FOR THE SuPPLY OF WaTER TO CiTIES AND ToWNS — II. WaTER AND THE

Foreign Matter usually Associated with it. — III. Rainfall and Evaporation. — IV.
Springs and the Water-bearing Formations of Various Districts. — V. Measurement
AND Estimation of the Flow of Water. — VI. On the Selection of the Source of
Supply. — VII. Wells. — VIII. Reservoirs. — IX. The Purification of Water. — X. Pumps. —
XI. Pumping Machinery. — XII. Conduits. — XIII. Distribution of Water. — XIV. Meters,
Service Pipes, and House Fittings. — XV. The Law and Economy of Water Works. —
XVI. Constant and Intermittent Supply. — XVII. Description of Plates — Appendices,
giving Tables of Rates of Supply, Velocities, etc., etc., together with Specifications
OF Several Works Illustrated, among which will be found : Aberdeen, Bideford,
Canterbury, Dundee, Halifax, Lambeth, Rotherham, Dublin, and others.

" The most systematic and valuable work upon water supply hitherto produced in English, or in
any other language. Mr. Humber's work is characterised almost throughout by an exhaustiveness
much more distinctive of French and German than of English technical treatises." — Engineer.

WATER SUPPLY OF TOWNS AND THE CON^

STRUCTION OF WATERWORKS. A Practical Treatise for the
Use of Engineers and Students of Engineering. By W. K. BURTON,
A.M.Inst.C.E., Consulting Engineer to the Tokyo Waterworks. Third
Edition, Revised. Edited by Allan Greenwell, F.G.S., A.M.Inst.C.E.,
with numerous Plates and Illustrations. Super-royal 8vo, buckram. 25s.

I. Introductory. — IL Different Qualities of Water. — I H, Quantity of Water to be
Provided. — IV. On Ascertaining whether a Proposed Source of Supply is Sufficient. — V.
On Estimating the Storage Capacity Required to be Provided. — VI. Classification of
Waterworks. — VII. Impounding Reservoirs. — VIII. Earthwork Dams. — IX. Masonry
Dams. — X. The Purification of Water. — XI. Settling Reservoirs. — XII. Sand Filtra-
tion.— XIII. Purification of Water by Action of Iron, Softening of Water by Action of
Lime, Natural Filtration. — XIV. Service or Clean Water Reservoirs— Water Towers —
Stand Pipes. — XV. The Connection of Settling Reservoirs, Filter Beds and Service
Reservoirs.— XVI. Pumping Machinery. — XVII. Flow of Water in Conduits— Pipes and
Open Channels.— XVIII. Distribution Systems. — XIX. Special Provisions for the Extinc-
tion OF Fires. — XX. Pipes for Waterworks. — XXI. Prevention of Waste of Water. —
XXII. Various Appliances used in Connection with Waterworks.

Appendix I. By Prof. John Milne, F.R.S. — Considerations Concerning the Probablk
Effects of Earthquakes on Waterworks and the Special Precautions to be taken in
Earthquake Countries.

Appendix II. By John De Rijke, C.E.— On Sand Dunes and Dune Sands as a Source of
Water Supply.

"We congratulate the author upon the practical commonsense shown in the preparation of this
work. . . . The plates and diagrams have evidently been prepared with great care, and cannot
fail to be of great assistance to the student." — Bziilder.

WATER SUPPLY, RURAL. A Practical Handbook on th6
Supply of Water and Construction of Water Works for small Country
Districts. By Allan Greenwell, A.M.Inst.C.E., and W. T. Curry,
A.M.Inst.C.E., F.G.S. With Illustrations. Second Edition, Revised.
Crown 8vo, cloth 5s..

"The volume contains valuable information upon all matters connected with water supply. . . »
It is full of details on points which are continually before water-works engineers." — Nature.

WELLS AND WELL-SINKING. By J. G. Swindell, A.R.LB. A.,
and G. R. Burnell, C.E. Revised Edition. Crown 8vo, cloth as*

30 CROSBY LOCKWOOD ^ SON'S CATALOGUE,

WIRELESS TELEGRAPHY: ITS THEORY AND

PRACTICE. A Handbook for the use of Electrical Engineers, Students,
and Operators. By James Erskine-Murray, D.Sc, Fellow of the
Royal Society of Edinburgh, Member of the Institution of Electrical
Engineers. Fourth Edition, Revised and considerably Enlarged, 450
pages, with 195 Diagrams and Illustrations. Demy 8vo, cloth.

Net I OS. 6d.

Adaptations of the Electric Current to Telegraphy — Earlier Attempts at Wire-
less Telegraphy — Apparatus used in the Production of High Frequency Currents —
Detection of Short-Lived Currents of High Frequency by means of Imperfect
Electrical Contacts — Detection of Oscillatory Currents of High Frequency by
their Effects on Magnetised Iron — Thermometric Detectors of Oscillatory Currents
of High Frequency — Electrolytic Detectors and Crystalline Rectifiers — The
Marconi System — The Lodge- Muirhead System — The Fessenden System — The Hozier-
Brown System — Wireless Telegraphy in Alaska — The De Forest System — The
PouLSEN System — The Telefunken System — The Level and other Shock-Excitation
Systems — Directed Systems— Some Points in the Theory of Jigs and Jiggers — On
Theories of Transmission — World- Wave Telegraphy — Adjustments, Electrical
Measurements and Fault Testing — On the Calculation of a Syntonic Wireless
Telegraph Station — Tables and Notes.

". . . . A serious and meritorious contribution to the literature on this subject. The Author
brings to bear not only great practical knowledge, gained by experience in the operation of wireless
telegraph stations, but also a very sound knowledge of the principles and phenomena of physical
science. His work is thoroughly scientific in its treatment, shows much originality throughout, and
merits the close attention of all students of the subject." — Etigineerin^.

WIRELESS TELEPHONES AND HOW THEY WORK.

By James Erskine Murray, D.Sc, F.R.S.E., M.I.E.E., Lecturer on
Wireless Telegraphy and Telephony at the Northampton Institute,
London ; Fellow of the Physical Society of London ; Author of " Wire-
less Telegraphy," and Translator of Herr Ruhmer's "Wireless Tele-
phony." Second Edition, Revised. 76 pages. With Illustrations and
Two Plates. Crown 8vo, cloth Nei is. 6cl.

How we Hear — Historical— The Conversion of Sound into Electric Waves — Wireless
Transmission — The Production of Alternating Currents of High Frequency — How the
Electric Waves are Radiated and Received— The Receiving Instruments — Detectors —
Achievements and Expectations— Glossary of Technical Words — Index.

WIRELESS TELEPHONY IN THEORY AND PRAC^

TICE. By Ernst Ruhmer. Translated from the German by
J. Erskine-Murray, D.Sc, M.I.E.E., etc. Author of "A Handbook
of Wireless Telegraphy." With numerous Illustrations. Demy 8vo,
cloth Net los. 6d.

"A very full descriptive a' count of the experimental work which has been carried out on Wireless
Telephony is to be found in Professor Ruhmer's book. , . . The volume is profusely illustrated
by both photographs and drawings, and should prove a useful reference Work for those directly or
indirectly interested in the subject." — NaUire.

"The explanations and discussions are all clear and simple, and the whole volume is a very
readable record of important and interesting work." — Engineering.

WORKSHOP PRACTICE. As applied to Marine, Land, and
Locomotive Engines, Floating Docks, Dredging Machines, Bridges,
Shipbuilding, etc. By J. G. Winton. Fourth Edition, Illustrated.
Crown 8 vo, cloth ... ... ... ... ... ... ... 3s. 6d.

WORKS* MANAGER'S HANDBOOK, Comprising Modern
Rules, Tables, and Data. For Engineers, Millwrights, and Boiler
Makers ; Toolmakers, Machinists, and Metal Workers ; Iron and Brass
Founders, etc. By W. S. HUTTON, Civil and Mechanical Engineer.
Author of " The Practical Engineer's Handbook," Seventh Edition,
carefully Revised and Enlarged. Medium 8vo, strongly bound 15s.

Stationary and Locomotive Steam-Engines, Gas Producers, Gas-Engines, Oil-Engines,
etc. — Hydraulic Memoranda: Pipes, Pumps, VV^ater-Power, etc. — Millwork: Shafting,
Gearing, Pulleys, etc. — Steam Boilers, Safety Valves, Factory Chimneys, etc.
— Heat, Warming, and Ventilation — Melting, Cutting, and Finishing Metals —
Alloys and Casting — Wheel-Cutting, Screw-Cutting, etc. — Strength and Weight of
Materials — Workshop Data, etc.

CIVIL, MECHANICAL. ELECTRICAL&'MAKINE ENGINEERING. 31

PUBLICATIONS OF THE
ENGINEERING STANDARDS COMMITTEE.

The Reports are Foolscap Folio, Sewed, except where otherwise stated.
Reports already published : —

1. BRITISH STANDARD SECTIONS (9 lists). {Included in No. 6).—

Angles, Equal and Unequal— Bulb Angles, Tees and Plates— Z
AND T Bars — Channels — Beams is. Net.

2. TRAMWAY RAILS AND FISH-PLATES 21s. Net.

3. REPORT ON THE INFLUENCE OF GAUGE LENGTH. By

Professor W. C. Unwin, F.R.S SS. Net.

4. PROPERTIES OF STANDARD BEAMS. {Included in No. 6.)

Demy 8vo, sewed ... ... ... . . ... ... ... IS. Net.

5. STANDARD LOCOMOTIVES FOR INDIAN RAILWAYS.

Superseded.

6. PROPERTIES OF BRITISH STANDARD SECTIONS. Diagrams

and Definitions, Tables, and Formulae. Demy Svo, cloth IS. 6d. Net.

7. TABLES OF BRITISH STANDARD COPPER CON^

DUCTORS 5S. Net.

8. TUBULAR TRAMWAY POLES ^s. Net.

9. BULL^HEADED RAILWAY RAILS 21s. Nei.

10. TABLES OF PIPE FLANGES 2S. 6d. Net.

11. FLAT'BOTTOMED RAILWAY RAILS 21s. Net.

12. SPECIFICATION FOR PORTLAND CEMENT ... 5s. Net.

13. STRUCTURAL STEEL FOR SHIPBUILDING ... 5s. l^^t.

14. STRUCTURAL STEEL FOR MARINE BOILERS ... 5s. ^^t.

15. STRUCTURAL STEEL FOR BRIDGES AND GENERAL BUILD^

ING CONSTRUCTION 5s. Aet.

16. SPECIFICATIONS AND TABLES FOR TELEGRAPH

MATERIALS 21s. Net.

17. INTERIM REPORT ON ELECTRICAL MACHINERY

19. REPORT ON TEMPERATURE EXPERIMENTS ON FIELD

COILS OF ELECTRICAL MACHINES ... los. 6d. Net.

20. BRITISH STANDARD SCREW THREADS ... 2s. 6d. Net.

21. BRITISH STANDARD PIPE THREADS ... 2s. 6d. Net.

22. REPORT ON EFFECT OF TEMPERATURE ON INSULATING

MATERIALS 5s. Net

23. STANDARDS FOR TROLLEY GROOVE AND WIRE is. Net.

24. MATERIAL USED IN THE CONSTRUCTION OF RAILWAY

ROLLING STOCK 21s. Net.

25. ERRORS IN WORKMANSHIP. Based on Measurements carried out

for the Committee by the National Physical Laboratory los. 6d. Net.

26. SECOND REPORT ON STANDARD LOCOMOTIVES FOR

INDIAN RAILWAYS Superseded

27. STANDARD SYSTEMS OF LIMIT GAUGES FOR RUNNING

FITS 5s. Net.

28. NUTS, BOLT<HEADS, AND SPANNERS ... 2s. 6d. Net.

29. INGOT STEEL FORCINGS FOR MARINE PURPOSES. 5s. Net.

30. INGOT STEEL CASTINGS FOR MARINE PURPOSES. 5s. Net.

31. STEEL CONDUITS FOR ELECTRICAL WIRING ... ss. Net.

32. STEEL BARS (for use in Automatic Machines) 2S. 6d. Net.

33. CARBON FILAMENT GLOW LAMPS 5s. Net.

P.T.O.

32 CROSBY LOCK WOOD 6- SON'S CATALOGUE.

PUBLICATIONS OF THE ENGINEERING STANDARDS COMMITTEE— (^^«/^.)

35. COPPER ALLOY BARS (tor use in Automatic Machines) 2S. 6d. Net,

36. STANDARDS FOR ELECTRICAL MACHINERY. 2s. 6d. Net.

37. CONSUMERS' ELECTRIC SUPPLY METERS (Motor Type for

Continuous and Single- Phase Circuits) ... ... ... ... 5s. Net.

38. LIMIT GAUGES FOR SCREW THREADS 5s. Net.

39. COMBINED REPORTS ON SCREW THREADS (containing

Reports Nos. 20, 28, 38) 7s. 6d, Net.

40. CAST IRON SPIGOT AND SOCKET LOW PRESSURE HEAT-

ING PIPES :2s, 6(X. Net.

41. CAST IRON SPIGOT AND SOCKET FLUE OR SMOKE

PIPES 2s. 6d. Net.

42. RECIPROCATING STEAM ENGINES FOR ELECTRICAL

PURPOSES 5S. Net.

43- CHARCOAL IRON LAPWELDED BOILER TUBES 2S. 6d. Net.

44- CAST-IRON PIPES FOR HYDRAULIC POWER ... 5s. Net.

45. STANDARD DIMENSIONS FOR THE THREADS OF SPARK-

ING PLUGS (FOR INTERNAL COMBUSTION ENGINES)

2S. 6d. Net.

46. KEYS AND KEYW AYS :ts. 6d, Net.

47. STEEL FISHPLATES FOR BULL-HEAD AND FLAT-BOTTOM

RAILWAY RAILS los. 6d. Net.

48. WROUGHT IRON OF SMITHING QUALITY FOR SHIP.

BUILDING (Grade D) ^s. 6d, Net.

49. AMMETERS AND VOLTMETERS 5s. ^V^/.

50. THIRD REPORT ON STANDARD LOCOMOTIVES FOR

INDIAN RAILWAYS, Incorporating Reports Nos. 5 and 26. 2 1 S. Net.

51. WROUGHT IRON FOR USE IN RAILWAY ROLLING STOCK.

" Best Yorkshire " and Grades A., B. and C I OS. 6d. Net.

52. BAYONET SOCKET LAMP-HOLDERS AND CAPS ... 5s. Net.

53. COLD DRAWN WELDLESS STEEL TUBES FOR LOCOMO-

TIVE BOILERS 2s. 6d. Net.

54. THREADS, NUTS AND BOLT HEADS FOR USE IN AUTOMO-

BILE CONSTRUCTION 2S, 6A. Net.

55. HARD-DRAWN COPPER AND BRONZE WIRE los. 6d. Net.

56. DEFINITIONS OF YIELD POINT AND ELASTIC LIMIT, Gratis.

57. HEADS FOR SMALL SCREWS us, 6 A, Net.

58. CAST IRON SPIGOT AND SOCKET SOIL PIPES .. 5s. Net.

59. SPIGOT AND SOCKET WASTE AND VENTILATING PIPES

FOR OTHER THAN SOIL PURPOSES s^. Net.

60. REPORT OF EXPERIMENTS ON TUNGSTEN FILAMENT

GLOW LAMPS (in two parts) ... ms, od. Net.

61. COPPER TUBES AND THEIR SCREW THREADS ... 2s. 6d. Net.

62. SCREWING FOR MARINE BOILER STAYS Gratis.

63. SIZES OF BROKEN STONE AND CHIPPINGS 3s. od. Net.

64. STEEL FISHBOLTS AND NUTS FOR RAILWAY RAILS.

5S. od. Net.

London: Crosby Lockwood & Son,

7, STATIONERS' HALL COURT, LUDQATE HILL, E.C.

and 5, Broadway, Westminster, S.W.

BRADBURY, AGNEW & CO., LD., PRINTERS, LONDON AND TONBRIDGE. 229. 20. II. I3.

•

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